Isn't the -in suffix in German supposed to make a noun feminine? So like 'heroin' would actually be a 'heroine,' i.e. the thing whose spelling is often confused

Isn't the -in suffix in German supposed to make a noun feminine? So like 'heroin' would actually be a 'heroine,' i.e. the thing whose spelling is often confused for it in English? I dunno, my German is schlecht. The thing about the "ba-ba-rians"... that sort of thing is everywhere. For example Slavs, as a certain people's name for themselves, seems to be related to the word "word" (slava or slova). They seem to be saying that a Slav is someone who speaks our language, i.e. someone who speaks words instead of that nonsense the others are always babbling!