Quomodo loquere in Latina “Please correct my mistakes”?
Saluē, Stancel!
The way to ask what something means is, “Quid sibi uelit?” litterally “what would it like for itself?”
“in Latin” or “in …” (whatever language), the adverb of the adjective is used, so since the adjective is Latīnus “Latin,” the adverb is Latīnē, meaning “Latinly,” or rather, “in Latin.” The same for “in English”: “Anglicē” from “Anglicus.”
As to your question, “Sī pr?uē dīc?, mē corrigite,” might be appropriate, “If I say incorrectly, correct me.” A more polite version of the imperative could be the present subjunctive: “mē corrig?tis,” “may you correct me.”
The word for “please” could be “quaes?” (I request) or “am?b?” (please, I beg). So all together, you might say, “Sī pr?uē dīc?, mē corrig?tis, quaes?.” The word for “mistake” is “mendum,” or possibly “error.”
Vale!
Gratias tibi ago 