In the 5th century AD, when first Germanic colonists made landfall in England, there was no Old English. All tribes arriving in the British Isles, spoke their own dialects, similar to each other but still variable. By the end of the century, however, when tribes turned into kingdoms, tribal speech became dialects. Three main ethnic groups which arrived in England spoke three dialects which got names of the kingdoms which were established by them. They were West Saxon (in Wessex, Essex), Northumbrian (in East Angeland), and Kentish (in Kent). West Saxon also includes the Mersian variety which had several slight differences in morphology and syntax, and more loanwords from Celtic, as Mersia was situated next to Wales with its Celtic population.

Dialects existed in kingdoms until they were independent. The richest literature was written in Wessex, but there are samples of documents also from Northumbria, Kent and Mersia, including poetry. After Aelfred unified all lands in 878, the dialects slowly integrated into one common tongue. But still even in Middle English period dialects were preserved, though their areas were changed somehow. And the Northumbrian dialect became a separate language - Scots, speaking nowadays in Lowland Scotland.

The most interesting of the dialects of Old English was Northern (or Nothumbrian). First of all it reflected the ancient speech of Angles, which is still poorly studied (unlike the Old Saxon language). Another interesting moment is that Northumbrian collected a rather wide vocabulary of borrowed words, mainly from Old Scandinavian, which really influenced Northern English greatly, and from Celtic. Several words from Northumbrian have some origin which is still unknown - they can be relics of the ancient population of the British Isles.

The Northumbrian grammar peculiarities are also interesting for an English speaker and especially for those who are learning the Scots language. Here are the main characteristic features of the Northumbrian dialect.

Phonetics
1. Practically no long [æ'] sound, and Saxon wæ're equals Northern wéron, etc.
2. u in open syllables is often pronounced like [y] (like in German fu''hlen), so Saxon cuman is Northumbrian cyman

Morphology
    a) -n in case endings of the Weak declension nouns is dropped, and the forms end in -u, -o, -a, -e. So in fact weak nouns lose the declension in the singular, and for example steorra (a star) will sound steorra in all four cases, while in Saxon it is steorran in genitive, dative and accusative. The same with sunne (the sun).
    b) Feminine ó-stem nouns take in the singular genitive the ending -es. In Saxon it is usually -e.
    c) The infinitive often ends in -a (drinca - 'to drink'). This is the direct Old Norse influence, and even today's Norwegian has this infinitive ending.
    d) the 1st person singular Present indicative ends in -u, -o (ic drincu - 'I drink') instead of West Germanic and Saxon -e.
    e) the 2nd person singular Present indicative and the 2nd singular Past indicative of Weak verbs ends in -s (þu drinces - 'thou drinkest'), while in Saxon it is -est.
    f) the 3rd person singular Present indicative ends in -s (hé drinces - 'he drinks'). This form was taken up by Middle English and therefore moved to the Modern English language.
    g) the plural indicative present ends in -as (hia drincas - 'they drink').
    h) the plural indicative past ends in -un (hia ségun - 'they saw')
    i) the plural indicative present of the verb béon is beoþan (we, you, they are).
    j) the plural of the personal pronouns is Nominative híá (they), Dative heom (them).
    k) the 1st participle sometimes ends in -ande again due to the Scandinavian influence.

Some strong verbs became weak in Northumbrian: class I - stígan (ascend), grípan (catch); class II - réocan (smell)  - past reohte, súpan (taste); class III - bindan (bind) - past binde, worpan (throw), fregnan (ask); class VI - hebban (lift) past hefde; class VII - sceadan (divide) - past sceadade.

All the rest dialects are not so peculiar, though have their special features as well. Kentish, for instance, has the -o ending in the 1st person singlualr of the Present tense (and 'I call' will be ic ható). You will be able to see all details of the dialectal speech in the text samples which are given in the paragraph below.
 

        Appendix I: Texts.

We decided to give examples of the several kinds of texts in Old English. This is made for our readers to realize how the language was used in the literature of the Old English period. That is why below you can find samples of the Saxon prose, short abstracts from the Old English Gospel (Saxon and Northumbrian variants), and two small texts in Kentish and Mersian dialects. Translations and glossaries follow the texts.
 

ylcan gere - the same year
worhte, worhton - it built, they built (from wyrcan 'to work, to build')
se - that (masc. nom. sg.)
foresprecena - above mentioned, aforesaid
here, herige - an army (masc. ja-stem)
geweorc - a fortress, a fort (neut. a-stem)
be, bi - by
bufan - above
byrig - a town, a city (fem. jó-stem)
sumer - a summer (masc. a-stem)
foron - they went (from faran 'to go')
micel - much, many
dæl - a part (masc. i-stem)
burgware - citizens
swa - so, so as, as
oþres folces - other folk (plural)
hie - they
gedydon, dydon - they did (from dón 'to do')
wurdon - were turned, were brought (from weorþan 'to become, to turn')
gefliemde - fleeing
sume - some
þegnas - thanes, servants (from þegn 'a thane', masc. a-stem)
ofslægene - were killed
hærfest - autumn, harvest (masc. a-stem)
wicode, gewicod - settled (from wician 'to dwell')
neaweste - nearness, neighborhood (fem. o-stem)
gerypon - they gathered harvest (from rípan)
ne mehton - they could not
ripes - harvest (genitive singular)
dæge - a day (masc. a-stem)
ea, eæ - water, a river (fem. consonant stem)
hwær - where
mon - a man, one
ut brengan - to bring out
scipu - ships (neut. a-stem)
tu - two (neut.)
on twa healfe - on the two sides, halfs
furþum - further
ongunnen - begun (from onginnan - to begin, to attempt)
onget - he / it understood (from ongietan - to understand)
forleton - they left, omit (from forlæ'tan - to leave)
eodon ofer land - they went over land (past from gán 'to go')
fird - a military expedition
ealle - all
stælwyrþe - serviceable
wæron binnan Lundenbyrig gebrohton - they were brought to London

Year 895. This very year built this above mentioned army [of Danes] a fortress by the Lygan [river] 20 miles above London. This summer a great part of citizens went, and other people with them, towards the Danish fortress, and there were put to flight, and some four [Danish] king's thanes were killed. Then this autumn the king settled near the town, and  at that time they gathered the harvest, which the Danes could not grow. Some day the king went to the river, and observed where people could work, [because] they could not bring the ships out. And they did so, they built two forts there, on both sides of the river. Then they had began [constructing] another fortress further, and there had settled. Then that army understood that they could not bring out the ships, so they left them, and went over lands and reached Cwatbridge on the river Safern, and there built a fortress. Then went the expedition after this army, and the men from London fought the ships, and could not sink all of them, but brought serviceable ones from there to London.

        Northumbrian (synonims of the specific Northumbrian words are given in brackets)
 1. and æfter sóne (hræþe) infoerde (inéode) capharnum  þé byrig æfter dagum and gehéred wæs þætte in húse wæ're.
 2. and efne cómon monige þus þætte né mæhte fóan (nioman) né tó dore /tó geáte/ and sprecende wæs heom (him) word.
 3. and cómon tóferende (bringende) tó him þone eorþ-crypel séþe from féowrum wæs geboren.
 4. and miþþý hí né mæhtun gebringan hine (him) for mengo genacadun (unwréogon) þæt hús (þá bere) þæ'r hé wæs and openedon (opnende dydon) ádúne sendun (settun) þá bere in þæ're þe eorþ-crypel læg (licgende wæs).
 5. miþþý gesæh þonne sé hælend geléafa heora cwæþ té þæm eorþ-crypele; sunu forgefen beoþan þé synne þíne.
 6. wéron wutudlíce þæ'r sume of uþwutum sittende and þencende (sméande) in heortum heortum.
 7. hwæt þes þus (swá) sprecaþ, hé folsaþ; hwá mæg forgeofan (forlétan) synne nymþe áne god.
 8. of þon sóna onget sé hæ'lend gást his þætte swá þohton (sméaldon) betwih heom cwæþ tó heom: hwæt þás gé þencaþ in heortum éowrum.
 9. hwæt is éþre (eaþur) tó cweþanne þæ'm eorþcryple; forgefen beoþun þé synne þíne; oþþe cweþan; árís and nim ber (bere) þíne and gáá.
 10. þæt wutudlíce witaþ gé þætte hé mæhte hæfeþ sunu monnes on eorþa forgefnise synne cwæþ tó þæ'm eorþ-cryple.
 11. þé ic sæcge: árís and nim bere þíne and gáá tó húse þínum.
 12. and instyde hé árís and under-léat bere, éode beforan allum swá þætte ofwundradun alle and þá worþadun god cweþende þætte hía næ'fre þus (swilc) né geségun.
 13. and færende wæs æfter sóna éc tó sæ' eall þá þréat cymende tó him and læ'rde hía.
 14. and miþþý þonan foerde gesæ'h ... sittende tó geafol-monunge and cweþ to him: folga (fylge) mé and árís fylgende wæs him.
 

        Modern English
 1. And when he returned to Capernaum some time later, word went round that he was back;
 2. and so many people collected that there was no room left, even in front of the door. He was preaching the word to them
 3. when some people came bringing him a paralytic carried by four men,
 4. but as the crowd made it impossible to get the man to him, they stripped the roof over the place where Jesus was; and when they had made an opening, they lowered the stretcheron which the paralytic lay.
 5. Seeing their faith, Jesus said to the paralytic: 'My child, your sins are forgiven'.
 6. Now some scribes were sitting there, and they thought to themselves,
 7. 'How can this man talk like that? He is blaspheming.Who can forgive sins but God?'
 8. Jesus, inwardly aware that this was what they were thinking, said to them, 'Why do you have these thoughts in your hearts?
 9. Which of these is easier: to say to the paralytic, "Your sins are forgiven" or to say, "Get up, pick your stretcher and walk"?
 10. But to prove to you that the Son of Man has authority on earth to forgive sins,' -
 11. he said to the paralytic - 'I order you: get up, pick your stretcher and go off home.'
 12. And the man got up, picked up his stretcher at once and walked out in front of everyone, so that they were all astounded and praised God saying, 'We have never seen anything like this'.
 13. He went out again to the shore of the lake; and all the people came to him, and he taught them.
 14. As he was walking on he saw [Levi the son of Alphaeus], sitting by the customs house, and he said to him 'Follow me'. And he got up and followed him.

geoue - a gift
wudumór - the big forest (from wudu 'wood', and Celtic mór 'big')
wynna bæce - the white brook (from Welsh gwin  'white')
seges - sedge
in wætan sihtran - marshy ground

That was after 500 winters and 189 winters since Christ was born, Offa the king in the thirty first year of his reign vgrants one hide of land to the monastery of Worchester for the brethren to own it as fully and forever, as I myself had.
I, Offa, through Christ the king of Mersia, with the Cross Symbol this my gift confirm. I, Edbert, the same thing confirm. I Bert the same confirm.
These are the boundaries from Bradewassan: from Temede stream to the white bridge, from the white bridge to Wudumor, from Wudumor to the marsh, from this marshy watercourse to the brook and from that brook to the old ditch, from the old ditch to the sedge lake and from the sedge lake to the pool's head, and from the head to Thornbridge, from Thornbridge to the pool and after the watercourse to Foxbridge, from Foxbridge to the wolfpit, from the pit to the old stile, from the stile to the Dodham pool, from the pool again to the Temede stream.

ferian - to become
cýþo, háto - I could, I had
wíb - a wife (= Saxon wíf)
liffest - while living
ober - over (= Saxon ofer)
brúcan - to let them use
mínre tíde - on my anniversary
mit heora godcundum gódum - in their divine service