Esperanto

... kaj ... kaj

Today I heard, for far from the first time, the expression "... ambaŭ ... kaj ..." used for "... both ... and ..."

This is an Anglicism and should be avoided. The correct expression is "... kaj ... kaj ...", as in

Mi nokte rigardas sur la ĉielo kaj planedojn kaj stelojn.
At night I look at both planets and stars in the sky.

The problem is, of course, that we learn ambaŭ as the Esperanto equivalent of the English both — and, in fact, when both is used by itself, that is the correct word to use. But when both is used in the combination shown, the correct equivalent is kaj.

There are two or three other such combinations, most of which do not give problems. The equivalent of "... neither ... nor ..." is "... nek ... nek ...", as in

Mi parolas nek la rusan nek la ĉinan lingvojn.
I speak neither Russian nor Chinese.

The equivalent of "... either ... or ..." is "... aŭ ... aŭ ...", as in

Por la Esperanto-Kongreso mi vojaĝos al aŭ San Diego aŭ Tijuana.
For the Esperanto Congress I will go to either San Diego or Tijuana.

A fourth, somewhat different and less commonly used form is "... kvankam ... tamen ..." for "... although ... nevertheless ...", as in

Kvankam estas jam malfrue, tamen mi ne dormas.
Although it's already late, nevertheless I'm not asleep.

Since the adverb tamen is very similar in its meaning and use to the conjunction sed, a lot of non-European Esperanto speakers, particularly Asians, use the form "... kvankam ... sed ..." This is wrong, but not illogical, and you will certainly encounter it more than once in your Esperanto-speaking career. For yourself, I recommend avoiding both forms and using the simple conjunction sed:

Estas jam malfrue, sed mi ne dormas.
It's already late, but I'm not asleep. (Yet.)