Needs native double-check !

English (and every language I can think of that is not French) doesn't use spaces before question marks, exclamation points, or other punctuation.

I would say:

Do you know if he is available? I need to know so I can make an appointment with him.

Thanks for your comment !

Question mark spacing :: corrected

Regarding the sentence you recommend, globaly I agree with it. However, I wonder if the original french sentence is translated in an exact manner : "disponibilités" is a noun, so should it be translated by an adjective ("available") ? Of course, if there is no noun in english which can express the fact of being available, or if it exists but is an old and uncommon word, then ok. In french "disponibilités" is very often used in formal contexts (especially on the phone). Could you please confirm that "if he is available" is also formal and used in such contexts ?

Concerning your advice of using "I need to know" instead of "I would need to know" (which sounds a bit weird, I admit), the original french phrase "j'aurais besoin" as compared to "j'ai besoin" implies some kind of distant/polite approach. It's a similar difference as in between "i want to have this" and "i would like to have this", in a weaker way though. Could you please confirm that "I need to know" can also be used in formal conversations ?

Cheers

> "disponibilités" is a noun, so should it be translated by an adjective ("available") ?

Translations should be natural, not word-for-word.

> Of course, if there is no noun in english which can express the fact of being available, or if it exists but is an old and uncommon word, then ok.

"Availability" exists and is neither old nor uncommon, but it would be strange to use it this way.

> In french "disponibilités" is very often used in formal contexts (especially on the phone). Could you please confirm that "if he is available" is also formal and used in such contexts ?

It's not formal, but it's not colloquial either. It's pretty neutral. (So you could use it in a formal context.)

> Could you please confirm that "I need to know" can also be used in formal conversations ?

Yeah, again, it's pretty neutral. If you want to make it sound slightly more formal than my suggestion, you could replace "so I can" with "in order to":

Do you know if he is available? I need to know in order to make an appointment with him.

Done !
Thanks for your help !