They mean exactly the same thing. "Language" is the normal word. Use "language" (and "native language.") The word "tongue" is use much more often to mean the organ in the mouth, than to mean "language." "Tongue," meaning language, is old-fashioned, poetic, and literary. It is the kind of word you read in fantasy or historical novels. You find it in books about King Arthur, or in the Arabian Nights, or the Bible: "a nation whose tongue thou shalt not understand." It is also a word that tends to be used about "primitive" cultures, because "language" is a little more respectful than "tongue." "Nations" have "languages," "tribes" have "tongues." I would never say "I am learning the Spanish tongue." And if I were filling out a form, I would write "English is my native language." I might say "English is my mother tongue," in the same half-joking way as I might say "I'm going to amble to the park" instead of "I'm going to walk to the park."

As far as I know, they are the same.

They will mean the same thing in certain contexts. For example, "English is my mother tongue" means the same as "English is my mother language." Tongue literally refers to what's in your mouth though, so in that sense "language" can't replace the word. Certain sentences sound a bit odd though. For example, we dont usually say "English is my first tongue" but we will say "English is my first language."

Hello, Maksim, There are 2 set phrases: "mother tongue" and "native language". They both refer to the language one has started learning from birth. But they are not identical: when using "native" the reference is more to the country/nation, when using "mother" the reference is to the parent (mother or father). The word "tongue" means also "a fleshy movable muscular part of the floor of the mouth". If you need more information about these words, write me and I will explain it in more detail.