I sampled some languages from a particular language learning app and here is my verdict.

Hardest to Easiest

Hindi, Korean, Thai

Japanese

Polish, Russian

Chinese, Arabic

English

Indonesian, Turkish

Afrikaans, Dutch

Danish, Swedish, Icelandic, Norwegian (Nordic languages)

Italian, French, Spanish, Portuguese, German.

Hindi, Korean and Thai are on top of the list simply because they don't use German alphabets. German alphabets are the common A-Z in English language.

Japanese comes second on the list although it seem like it would be quite easy with the right learning resources.

Personally, I think you will have to go to a language school to learn Polish and Russian. The spelling and pronunciation differs in ways you would not expect.

Chinese and Arabic both come across as "easy" if you can dedicate time to learning them.

English is hard, enough said.

English hard gon

You can only make comparison based on which language is closest to your original language. No language is easy to learn. None. Especially international languages where you have to learn structures for literacy purpose. A Korean will say Chinese is the easiest language to learn and a Spanish will say Italian.

The closest languages to English are Dutch, German, Spanish, Italian, Portuguese and French only that they all have gender.

Among these closely related languages German and Dutch for me is easiest because of the lack of strong accent and the easy pronunciation. Then of course Spanish, Italian and Portuguese. Easy pronunciation patterns, and even with the heavy accent of these languages once you've gotten the rhythm then you are good to go. French comes in last solely because of the heavy syntax in the language and you do not pronounce half the words written so they end up sounding the same, then there's a lot of merging of words.

But what to keep in mind is, It's not impossible to learn any international language, just time and effort is required.

I have tried to learn a few of the languages you posted and for me the easiest is Chinese.

Learning to speak Chinese is really easy, it doesn't have nearly as much grammar rules as so many other languages.

The difficult part is learning to write Chinese characters. Now that is difficult. With constant practice you would be able to recognize them but writing is not easy atall. I suppose that's why many people opt for pinyin.

2nd English, 3rd Spanish, but that's probably because I already speak French.

4th Portuguese.

I tried learning Japanese but couldn't sustain my interest.

French is among the difficult. too many rules.

At the end of the day, it all depends on the person. This is just me.

I'm trying to learn Spanish and French and I think french is more difficult because I started learning it way before I started learning Spanish yet I still can't grasp the rules of the language.

French is the easiest. Most words in English are in french. I recommend the podcast from Michel Thomas for any one who wants to learn French. I'm on an intermediate stage I'm just building my vocabulary.

Learning any international language,is a thing of the mind.You learn language with your heart and not with your brain.