Some difference may appear if you want to put more words in the sentence. Strictly, "I liked speaking in French" is "Mi sxatis paroli en la franca" or "Mi sxatis paroli france" (this last one seems to be more usual). For example, maybe I liked speaking some things in French, so this has to be "Mi sxatis paroli iujn aferojn france/en la franca" (while "Mi sxatis paroli iujn aferojn la francan" is totally wrong).
Let me see if I understood you correctly.
"Mi ŝatis paroli la francan" would be "I liked to speak French"? because 'paroli' is in the infinitive and that the equivalent form in English is 'to speak', right?
"I liked speaking in French" would be "Mi ŝatis paroli france" because 'in French' (-> france) acts like an adverb modifying the verb prhase 'liked speaking' (-> ŝatis paroli).
That's more or less it, right?