There are several possible variations to these answers depending on the meaning you're trying to convey and your writing style but below is what I propose. I've added a grammatically incorrect English translation afterwards to show you the difference in meaning from your original sentence. 1- "J'apprends l'allemand depuis cinq ans mais je dois encore le pratiquer." (I am learning english since 5 years but I still need to practise it) There's no clear verb equivalent for "have been" in French. In this case, you can use the present verb tense of "apprendre" (to learn) and follow with "depuis 5 ans" to explain that you started learning 5 years ago and it's still on-going. When it comes to the second part of the sentence, you can alter the meaning of the sentence by substituting the adverb "encore" with "toujours", or "quand même" even. 2- "N'hésitez pas à me demander quoique ce soit par rapport à la langue chinoise." (Don't hesitate to ask me anything in relation with the chinese language) "N'hésitez pas" (Don't hesitate) is the closest translation of "Feel free to..." in my opinion. If ever you're addressing the sentence to a person you personally know, you can write "N'hésite pas" instead.

You could say : "J'étudie l'Allemand depuis 5 ans, mais j'ai encore besoin de m'entraîner/pratiquer." And : "N'hésitez pas à me demander/questionner pour tout ce qui a un rapport avec la langue Chinoise."

J'étudie l'Allemand depuis 5 ans, mais je n'ai pas de temp pour pratiquer.