I think it is mother language)

Sign language is the eastist i think.

Although as a speaker of Esperanto I would advocate Esperanto as the easiest, Esperanto aside it would vary from person to person. It generally depends on which languages you are exposed to, for example I (in England) would probably find German or French easy, because of their geographical and linguistic proximity to English, but a bilingual Tagalog/English speaker may perhaps find Cebuano or Spanish easier.

I think the language easiest to learn is spanish. I have more difficult to learn english! I'm French 

Here in the U.S., the language considered the easiest to learn is Spanish. Since Spanish and English are both derivations of Latin, there are many commonalities. Much of the language is straight-forward, with masculine and feminine nouns. When taking courses at the military's Defense Language Institute, Spanish is amongst the shortest of courses. Perhaps others will disagree.