Looking at the Kaddish Shalem focusing on the words תִּתְקַבֵּל צְלוֹתְהוֹן, what is the etymology of the word tzelot-hon? Is this construct even hebrew? I found the root צְלָא meaning "pray" with explanation: "Aramaic, probably corresponding to צָלַע [tsala` ] in the sense of bowing". Come to think of it, there is a lot of construct in this prayer that doesn't coincide with biblical hebrew. Is the entire prayer in Aramaic? Is there any commentary on these obscure words?
The entire prayer, except for the last line, is in Aramaic.
צלי, צלא, or צלו are different constructs of the word meaning "pray". צלותהון means "their prayers".
As for the root, I believe it is likely correct that it is צלא, though a part of me wants to go digging in my old Aramaic text books to rule out the possibility that it is צלי.
I have never heard it suggested that it comes from a lost guttural (צלע), so I would like to see the source that you read about that.
The root of the word is צלי, which means "to turn" or "incline", and which has the sense of "pray" in many passages. For the former, see the Targum on Psalm 102:12 (where it corresponds to the Hebrew word of root נטה), and for the latter see Targum Onkelos on Genesis 12:8 (where it corresponds to the Hebrew word of root קרא). When it means "pray", it is always in the pael - which is an Aramaic stem that roughly corresponds to the Hebrew piel.
As a noun, however, it appears in Old Aramaic as צלו, and in Late Aramaic as צלותא, the latter being with the addition of the definite article for a feminine noun. You can find that word in Onkelos on Genesis 18:22, for example, where it describes Abraham occupying himself "in prayer" before God (with no corresponding Hebrew expression). The plural, צליין (or צלותיא, with the definite article) can be found in the Targum on Psalm 72:20, in which it corresponds to the Hebrew תפלות.
The word צלותהון comprises the singular noun, "prayer", plus a 3rd person masculine plural suffix (הון-), meaning "their prayer". The verb that appears before it in your nusach (תתקבל) is a 3rd person singular feminine imperfective: "may their prayer be received". I understand that it is usually translated in the plural ("may their prayers be received"), but while this would probably require the noun to appear as צלוותהון or צלייתהון (I'm not sure if these forms are attested), it would certainly require the verb to appear as תתקבלן, with a final nun.
צְלוֹתְהוֹן means praying in Aramic. Many other words of Kadish are also Aramic.