S-Tier
English: Extremely easy to learn because of very basic functional grammar, 48% of its vocabulary is Latin based (derived from French), learning this first will help massively learn all other neo-latin languages, spread everywhere in the world
Spanish: It is English but fully Neo-Latin for all of Southern America (very easy grammar)
French: Harder than Spanish but still spoken a lot around the world (Arabic people use it as Lingua Franca) and easy to learn if Spanish is properly known
Portuguese: Spoken in Portugal, some African countries, some of Japan and all of Brasil, very easy to learn but less important than Spanish
B-Tier:
Russian: It is the English language of the Russian Ex-Federation countries, but It is HARD and requires much more time than the others, also English is still learnt by Russians so it loses importance
C-Tier:
German: French\English are also spoken in the coutnries where German is a second\third language, only learn if you go living in Germany
Italian: Only spoken in Italy for real, least important true neo-latin language to learn but has the richest vocabulary out of them
Arabic: Spoken in all Arabian countries which are many so C-Tier for that, but extremely dififcult to learn as non-native
Indian (and variations):
Everybody speaks Englsih in India, C-Tier because second spoken in the world as native langauge, otherwise don't bother
D-Tier:
Korean\Japanese: very hard and totally pointless regarding business as English is spreading in Korea\Japan, only learn if interested in living there, only spoken in respective countries
F-Tier:
Chinese: Once an estimable language (Ancient China history was full of beacons and erudites), today is the de-facto oppressors language, in China business people use English, don't even bother
That's it.