There is the word 'tongue' which replaces 'language' in some contexts, such as 'mother tongue' - one's first language.
There is no single-word synonym for "their" in the English language.
Yes it is, tongue and mother tongue as a synonym.
the synonym for the word above is learing
principal
the same
Language or nomenclature.
A Linguist.
Argot is a French, Spanish, and Catalan word meaning "slang." So I suppose the synonym would be "slang." It is also a secret language, so secret language could be another synonym for it.
There isn't such word in the english language.
partnership = Partnerschaft
Many languages have these.
No, actually "grammer" is a common misspelling of the correct word, grammar. A synonym phrase for grammar might be "structured language".