"He likes the girlfriend."
Translation:Er mag die Freundin.
"gern haben" means to like. I don't think many Germans would use "mag" in this instance.
Sorry, some days ago I wrote a reply which I deleted after about two seconds because I hadn't read your question carefully. I don't know if you still saw it, though (?). Yes, "gern haben" would also work in this sentence. But so does "mögen".
Is there a difference in the meaning between these:
Er mag die(seine) Freundin. Er hat die(seine) Freundin gern. Ihm gefällt die(seine) Freundin.
Is any of these rather unusual or impolite? (I added "seine" because die sounds very odd to me for this context)
Doesn't gefallt mean "liked" since the ge- prefix generally indicates past tense? Thus, wouldn't "Die Freundin gefallt ihm" not be a choice?
The word 'gefällt' comes from the verb 'gefallen,' so even though it starts with 'ge-' it is present tense in this sentence. 'Gefallen' also happens to be the past perfect tense of the verb, so past tense sentence would be 'Die Freundin hat ihm gefallen' or 'Ihm hat die Freundin gefallen.' Another option for the past tense would be 'Die Freundin gefiel ihm' or 'Ihm gefiel die Freundin.'