"My dog is dirty."
Translation:Tá mo mhadra salach.
No, but you might be able to use sailíocht (“dirtiness”) rather than salach (“dirty”) in that sentence.
In plural forms, but then I not sure, what qualifies as plural.
Personal thinking is, it should be:
"Níl siad oifigiúila", not "Níl siad oifigiúil."
"Tá na dathanna difriúila." not "Tá na dathanna difriúil."
Or "Tá mo dheirfiúracha difriúila." rather than "Tá mo dheirfiúracha difriúil."
Only attributive adjectives are modified in the plural, e.g. Tá na boscaí móra ansin. but Tá na boscaí mór.
The plural adjective is lenited after a noun the plural of which is formed by placing an 'i' before the final consonant ('ch' will usually become 'gh'), e.g. Na fir shalacha, Na fathaigh mhóra.
Thanks, I was already afraid, that all exceptions were ending in "-iúil" (or that pronouns are an exception). This really had bothered me for some time.
Having the attributive adjective sinking in will take a couple of months, but I can relate to that now.