English counting is largely regular, with a couple of small historical exceptions right at the start that trip up learners more than the rest of the system combined.
Thirteen through nineteen follow a clear pattern (three+teen, four+teen), but eleven and twelve don't — they come from older Germanic words roughly meaning "one left over" and "two left over" (past ten), rather than fitting the "-teen" pattern the way "thirteen" does.
From twenty onward, English numbers combine tens and units in a simple, additive way ("twenty-one," "thirty-five"), matching the same underlying logic used in many other languages, including Turkish's otuz bir (see Turkish Numbers).
They come from older Germanic words roughly meaning "one left over" and "two left over" past ten, rather than fitting the regular "-teen" pattern used from thirteen onward.
Yes — they combine tens and units in a simple, additive way ("twenty-one," "thirty-five"), the same basic logic used in many other languages.
In terms of noun agreement, yes — English doesn't change the following noun's grammatical form based on the number the way Russian case agreement or Arabic gender-reversal do.
Yes, as core vocabulary content, matching the approach used in Tarc's existing courses.
See also: English Vocabulary · English Grammar · Learn English