Why is "Gàidhlig" sometimes capitalised and sometimes not?
Every sentence containing the word has a capital. The software itself draws on the entire bank of words (including places, names and languages) and does not always capitalise.
Probably a typo
Is there a reason why this sentence is translated "i have gaelic" instead of "i speak gaelic"? I understand that it's direct translation of the sentence, but that's not how you would say it
It actually is how many would say it, and the course creators are, by and large, Scots who speak Gàidhlig.