A language with conjugation rules for words of any kind (n., (ad)v., adj., etc...)
Randomly, and during the passing period in university after my second class (which should've started but apparently was postponed since my instructor didn't show up and didn't let us know about it), I was thinking of a fictional language.
The language, though not Spanish, is inspired by the Spanish language where it uses these conjugation rules for present-tense verbs (regular and irregular), but they can be applied to all types of words such as nouns, adjectives, adverbs, and whatnot. The language.
These conjugation rules apply for each subject in first person (I), second person (you), second person plural (you all) and third person specific ([name]/(s/t)he(y)), first person plural (we), and third person plural (they), similar to those such as the Spanish subjects for yo (1st), tú (2nd informal), usted [él/ella] (2nd formal plural/3rd specific), nosotros/as (1st plural) vosotros/as (2nd Spain), and ustedes [ellos/as] (3rd plural).
Normally, these would apply to mostly present-tense words/phrases because these are more common in those, but you could apply these to past-tense and future-tense words/phrases.