Is knowledge of the local language, such as French for France, mandatory for studying and working part-time there for a Master's?

No, knowledge of French is not mandatory to study in France, especially if you choose an English-taught master's program. Many universities offer courses in English for international students.

However, for part-time work, basic French is often needed. Most part-time jobs in retail, hospitality, or customer service require at least conversational French, while some on-campus roles may not.

You can legally work up to 964 hours/year (about 60% of full-time) with a valid student residence permit. Learning French will make it much easier to find part-time work and adapt to daily life.