In maltese :
-/ʕ/ and /ɣ/ have merged into 'għ'. How is it pronounced?
-/ḥ/ and /χ/ have merged into 'ħ'. How is it pronounced?
I've tried multiple youtube videos and :
-'għ' sounded nothing like /ʕ/ or /ɣ/ but like an 'a'.
-'ħ' sounded nothing like /ḥ/ and /χ/ but like an 'h'.
Makes me think that those speaking in these videos are not native speakers.
You might try Forvo.'ħ' is like Arabic 'ħ', but can be a bit different (but ħ is not really phonetically identical across all Arabic dialects). Likewise ħ (spelled x) in Somali is a bit different. Orthographic 'għ' is not standardly pronounced 'as such': this is the subject of a classic article by Mike Brame. Basically /ʕ/ behaves like ʕ throughout much of the phonology of Maltese, but then is vocalized to [a], deleted, or turned into [ħ] depending on context. There is much variation in Maltese dialects, and there are reports of dialects where ʕ is retained (a few hundred years ago).
In the International Phonetic Alphabet, this sound is written /ħ/ (conveniently enough): a voiceless pharyngeal fricative.
Since you mention ḥ, I'm guessing you've studied Arabic or a related language? It's like English /h/ but with a lowered larynx, or Arabic ح. /ħ/ is usually written ḥ when transcribing Arabic, though I personally prefer writing ħ.
This letter has a few different pronunciations. At the end of a word or before h, it's like ħ, but longer. Before a vowel, it lengthens and pharyngealizes it. According to Wikipedia, "għi and għu are [aˤj] and [oˤw]".
