Both Gaelic and German are Indo-European languages, but so are Spanish, the Slavic Languages, and Sanskrit; so the differences are pretty large. English is a germanic language, with a lot of additions from other languages along the way and a loosening of the grammatical rules. You will find a lot in German to remind you of English, and a lot (especially in the grammar) which will be very foreign to you because German adopted and adapted a latin grammarical structure somewhere along the line.