How do you translate speak French only English into French?

This is a bit tricky because the phrase "speak French only" is a bit ambiguous. It could mean:

* "Parlez uniquement français." (Speak only French.) This is the most direct translation.

* "Ne parlez que français." (Speak only French.) This is another way to say the same thing.

* "Français seulement, s'il vous plaît." (French only, please.) This is a polite way to ask someone to speak French.

The best translation depends on the context. If you are giving a command, the first two options are best. If you are making a request, the third option is more appropriate.