Except for when you acquire another language, or other languages as a young child - and are almost certainly not fully aware of the concept of 'another language' - learning your first foreign language involves some startling things. For somebody in whose own language negation is expressed by the equivalent of "I love not", "I not love" or "I no-love", the English "I do not love" is weird. It may take a long time to accept this; however, once it has been accepted, learners are not quite so shocked when they meet, in their second foreign language "I ne love pas". If, in their third foreign language, the negative turns out to be the equivalent of "I evol", well, so be it. The systems still have to be mastered, but they are no longer seen as outlandish.
That said, I do feel that it is almost certainly easier if your second foreign language is in the same language family. Thus, I would say that if a speaker of an African language, for example learnt French as their first foreign language, then they would find the difficulty of learning the second foreign language something like this:
Italian - easy. Italian and French are closely-related Romance languages.
Romanian - less easy. Romanian and French are both Romance languages, but not so closely related.
English - more difficult; English and French are both Indo-European languages, but different branches. However, English and French have a lot of vocabulary in common.
Czech - decidely more difficult. Czech and French are both Indo-European languages, but vey different in vocabulary and surface structure.
Turkish - very difficult. Turkish is not an Indo-European language, and both vocabulary and grammar are very different.