"This is a sweater."
tha seo geansaidh does not make any grammatical sense. You can’t use the verb tha here, you need the copula is, which is often omitted before seo and sin.
See those discussions explaining this:
- Seo vs Tha seo: https://forum.duolingo.com/comment/38564893
- "Tha sin dona.": https://forum.duolingo.com/comment/35388178?comment_id=35388600
- "This is a good picture.": https://forum.duolingo.com/comment/37019399?comment_id=37019654
Actually, in English cat comes from Proto-Germanic *kattuz, in Scottish from Old Irish catt which was borrowed from Latin cattus, Polish kot comes from Proto-Slavic *kotъ which in turn might be borrowed from either Germanic or Latin…
Latin and Proto-Germanic took the word from somewhere – uncertain where, and one of them probably borrowed it from the other. So all those words are somehow ultimately related, but in this particular case, neither English borrowed it from Gaelic, nor Gaelic from English.