Of speech or language: offensive, obscene; containing swearing or rude words; (also) abusive. Also occasionally in weaker use: unpolished, inelegant…

spec. Of language, a word, etc.: incorrect, wrongly used. Formerly also: †figurative, not literal (obsolete). Now rare.

Containing or characterized by errors, faulty; (later also, of a guess, etc.) erroneous, wrong.

figurative ? Foul, unclean; ? rude, uncultured.

Impaired or spoiled by some fault, flaw, blemish, or defect; faulty, defective, imperfect, bad… Of language, style, spelling, etc. Also transferred…

of language: Imperfectly spoken, with the syntax incomplete.

Wrong, incorrect, improper. Obsolete. rare.

Solecistic.

Contrary to or not conforming to a rule or rules; irregular.

Of the nature of or involving solecism. In speech or diction.

(un-, prefix1 affix 1.)

That does not come naturally to a native speaker of the language; unidiomatic.

That has been murdered (in various senses of the verb).