Tha beagen Gaidhlig agam
Does that mean - I "speak" only a little Scottish Gaelic ?
If so, why agam here ?
And if that is the case, why the translations says "have"... which doesn't seem correct in modern day English.
Gaelic does not have a word for 'have.' It's represented by the particle 'ag' / preposition 'aig'.
In the case of "agam," it is the first person singular of the word, indicating that you have something, or 'can (do) something.' Literally, "agam" is like saying "at me/of me" in English.
So "Tha Gàidhlig agam" > Is Gaelic of me > Is Gaelic I have > I speak Gaelic.