πριν αβρααμ γενεσθαι εγω ειμι [TR] John 8:58 [Text undisputed]
Baxter's Analytical Greek Lexicon says of the word γενεσθαι, genesthai, that it is the aorist 2, infinitive and is an inflection of γίνομαι, ginomai Strong 1096 which means 'to come' 'to become' or 'to come into being'.
And, without a doubt, the meaning of εἰμί, eimi Strong 1510 is 'I exist' or 'I am'. It is, in the text, the first person singular and the present form of the verb. It cannot be made to mean anything other than 'I am' or 'I exist' whatever may precede it or whatever may follow it. It means what it means.
YLT (Young's Literal Translation) translates the verse :
Before Abraham's coming -- I am;
And the KJV gives :
Before Abraham was, I am.
Green's Literal Translation has :
before Abraham came into being, I AM.
J N Darby has the same as the KJV :
Before Abraham was, I am.
Douay Rheims gives :
Before Abraham was made, I am.
I would have expected The Wycliffe to be as D-R (since they are both from the Vulgate) but Wycliffe has :
Before that Abraham should be, I am.
I would suggest, myself, that 'before Abraham was to come' is also faithful both to the aorist and to the infinitive.
That Jesus says, 'before Abraham' . . . I am' cannot be considered ungrammatical from an English language point of view. It is an expression of eternal being. Which is not a matter of a past tense 'I have been'.
The eternal is. It changes not.
It is perfectly correct to say 'I am' if one is indeed, as he is, eternal.
One can change the sentence around and say 'I am, before Abraham was' and it means exactly the same thing. The statement 'I am' is not dependent on what, originally, preceded it or what, now, follows it. There is an equivalence.
The preposition πριν, prin, 'before' modifies the clause 'before Abraham came' or 'was' but it does not affect the main statement 'I am'. It governs its own clause. Before this . . . that. Or, that . . . was before this.
The copular verb εἰμί, eimi, 'I am', is first person singular and it is present tense. It cannot be made into a past tense, of any kind, by the preposition which governs the clause regarding Abraham.
Whether or not Jesus is naming himself as Jehovah in this particular place is wholly another question which I do not wish to encroach upon in this particular enquiry.
But no, it is not ungrammatical and it is not 'pidgin' according to the definition stated by Wikipedia.
It appears to me that an attempt is being made to mistranslate Jesus' words by criticising the quite correct translation 'I am'. By saying that the correct translation is 'ungrammatical' or 'pidgin' English, the real criticism is, in fact, a criticism of what Jesus actually uttered.
If the translations above that I have cited are - indeed - valid, grammatical and correct translations, then Jesus did, in fact, say (in the Greek language) 'I am'.