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"to" and "two" are just too similar in englihs, perhaps they should use some other sign or language for nearly homophonic words

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“to” is instructed not to be used in pilot/atc conversations, for this reason.

For example: descend and maintain flight level three two zero

Same goes with “for”, which you sometimes hear in readbacks like “leaving 4000 for 3000”. It should be something unambiguous like “4000 descending 3000” instead.

However “cleared for takeoff” is standard.

It is hard to see how that one can be ambiguous.

This is one of the explicitly unambiguous phrases introduced after https://en.wikipedia.org/wiki/Tenerife_airport_disaster#Prob... ; note that the meaning of "cleared for (allowed to) takeoff" is completely different from "leaving 3000 for (to the new level of) 2000". In essence, a different word entirely; one of the reasons it is avoided except in complete, unambiguously defined phrases.

Quoth Wikipedia: The word "takeoff" is now spoken only when the actual takeoff clearance is given, or when cancelling that same clearance (i.e. "cleared for takeoff" or "cancel takeoff clearance"). Up until that point, aircrew and controllers should use the word "departure" in its place (e.g. "ready for departure").

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