So, theoretically, English could be something like this:
Consonants:
Ff - like f except between vowels, where it's a v sound
Ȝ ȝ - a y sound
þ - beginning and end of words, as 'th' in 'think'
ð - between vowels, as 'th' in 'that'. The þ will turn into ð in nouns when adding an ending on the word (Pæþ to Pæðen)
Gg: hard 'g' before a/o/u, soft 'g' before e/i
Consonant clusters:
sch: sh
ȝh after e/i/æ/y, like German ich; after a/o/u like German ach. It lengthens the vowel before it
Definite Article:
the/that:
þe (þes, þen) (masculine)
þe (þer (d/g), þe (a)) (feminine)
þat, þes, þat) (neuter)
this:
þiss, þisses, þissen
þisse, þisser, þisse
þiss, þisses, þiss
Masculine Nouns:
(s) (N G D/A): Stoon, Stoon(e)s, Stoon, Stoon (stone)
(p) (N G D/A): Stones, Stones, Stonen, Stones
Most masculine nouns are like Stoon; those ending in 'e' are 'weak':
(s) (N G D/A): Appe, Appen, Appen, Appen (ape)
(p) (N G D/A): Appen, Appen, Appen, Appen
similarly Ange, Bane, Beene, Snake, Slage, Plege, Nake, Name, Nefe, Mage, etc.
Feminine Nouns:
(s) (N G D/A): Gaat, Gaat, Gaat, Gaat (goat)
(p) (N G D/A): Gæte, Gæte, Gæten, Gæte
Most feminine nouns just add (e)n in the plural, like all nouns ending in -ung
(s) (N G D/A): Riȝhtung, Riȝhtung, Riȝhtung, Riȝhtung (direction)
(p) (N G D/A): Riȝhtungen, Riȝhtungen, Riȝhtungen, Riȝhtungen
or in 'e':
(s) (N G D/A): Strenge, Strenge, Strenge, Strenge (strength)
(p) (N G D/A): Strengen, Strengen, Strengen, Strengen
similarly: Nose, Saule (soul), Swaðe (track), Snore (daughter-in-law), Nafe (nave of a wheel), Are (honor), Gefe (gift)
Otherwise, they just add 'e' at the end:
(s) (N G D/A): Kwen, Kwen, Kwen, Kwen (queen)
(p) (N G D/A): Kwene, Kwene, Kwenen, Kwene
similarly, Hand
The feminine nouns ending in -nes or -en or -et, add -se/-ne/-te in the plural. (Westen, desert; Fæsten, fortress; Bærnet, arson, etc)
Neuter Nouns:
(s) (N G D/A): Lamb, Lambes, Lamb, Lamb (lamb)
(p) (N G D/A): Lamber, Lamber, Lambern, Lamber
like lamb, Child, Speld, Kalf, and older neuter nouns that had no inflected plural (Kynn, Bedd, Bill, Wedd, etc). Former neuter nouns ending in 'en' became feminine around 1300.
(s) (N G D/A): Knee, Knees, Knee, Knee (knee)
(p) (N G D/A): Kneen, Kneen, Kneen, Kneen
Knee used to have an uninflected plural, but took the weak 'n' ending of Eaȝe (eye), Eare (ear), Wange (cheek), and dozens of other neuter nouns (Tree, Straw, Saw, Lee, Hree, Low, Bee, Anklee, etc), and neuter nouns ending in -el and -er (Tungel, star; Wunder, wonder, etc)
Pronouns:
I: ik, mein, me
thou: þu, þein, þe
he: he, his, him, him
she: sche, her, her, her
it: it, his, him, it
we: we, ur, us
ye: ȝe, ȝoer, ȝo
they: þeiȝ, þeir, þeim
Adjectives:
after definite articles:
M N F PL
N e e e en
G en en en en
D en en en en
A en e e en
unpreceded:
M N F PL
N e e e e
G es es er er
D en en er en
D/A en e e e
Comparative, Superlative:
always add er, est to an adjective:
blind, blinder, blindest
Irregular:
god, better, best
lyttel, læss, læst
Michel, mær, mæst
yfel, wiers, wierst
Strong Verb example:
helpen: to help
present indicative:
ik helpe we helpeþ
þu helpst ȝe helpeþ
he helpþ þeiȝ helpeþ
present subjunctive:
singular: helpe
plural: helpen
he sæȝde þat schie helpe him (he said that she is helping him, but I can't verify it)
past indicative:
ik halp we halpen
þu halpst ȝe halpen
he halp þeiȝ halpen
past subjunctive:
singular: hulpe
plural: hulpen
Example: if þu hulpe me, we kunnen soner gaan: if you would help me, we can go sooner.
past participle: holpen
Ik habe holpen, þu hast holpen, etc.
finden - to find; fand, funden
baken - to bake, bok, baken
standen - to stand; stod, is standen
been - to be; em, ert, is, sind; was, wast, was, waren; is been
Weak Verbs:
demen - to judge
ik deme we demeþ
þu deemst ȝe demeþ
he deemþ þeiȝ demeþ
subjunctive: deme, demen
past (add -de):
ik demde we demden
þu demdest ȝe demden
he demde þeiȝ demden
subjunctive: demde, demden
past participle: dem(e)d
ik habe demed/deemd
Preterite Present:
witten - to know (waat, wiste, witten)
durren to dare (daar, dorste, durren)
Modals:
kunnen to be able, know how to, can (kann, kuðe, kuþ)
magen to have permission to, may (mæȝ, mihte, miht)
moten to have to, must (mot/most, moste, most)
willen to want to (will, wollde, wolld)
schullen to be obligated to, ought to, shall (schall, schollde, scholld)
þurfen to need to (þarf, þorfde, þorfd)
ik kann we kunnen
þu kannst ȝe kunnen
he kann þeiȝ kunnen
So, that's my theoretically more conservative English. It looks like Late Old English/Early Middle English around 1100-1200 or so.