How can 'for' be translated correctly in French?

When translating for in French, we have to take into consideration the three prepositions which can be used: depuis, pendant and pour. The one which is selected depends on the situation and the action being described in the phrase and must be accompanied by the appropriate tense. When we are speaking about an action which has started in the past and has not yet been completed, we use the present tense with depuis. For example: I have been studying french for ten years translates as J'étudie le français depuis dix ans.When an action which started in the past and was still ongoing when it was interrupted by another action, we use the imperfect tense with depuis.For example: She had been studying French for 5 years when she watched her first french film becomes elle étudiait le français depuis cinq ans quand elle a vu son premier film français. However, when translating actions which lasted for a period of time and are completed, we use pendant with past tenses such as le passé composé or le plus-que-parfait.For example: she studied German for three years at school translates as elle a etudié l'allemand pendant trois ans à l'école. When translating events regarding the future (and never past completed events), we use pour and the present or future tenses. For example: I'm going to England for two weeks is translated as je vais partir en Angleterre pour deux semaines.