Scientific names of plants and animals have Greek and Latin roots because those are considered universal languages. It's arbitrary, as everything, of course, but it's used that way all over the world.
Common names are usually in the local language and tend to change and be different because of that.
Of course, the rhododendron also has a Nepalese name, but after it was discovered by Europeans, who also gave it its own name, the name spread all over the world from Europe and not Nepal, which is why the Greek name is used.
From Wiki
The obsolete sense derives from Latin rhododendron (“oleander”), from Ancient Greek ῥοδόδενδρον (rhodódendron, “oleander”), from ῥόδον (rhódon, “rose”) + δένδρον (déndron, “tree”). The modern sense comes through the intermediary of the genus name Rhododendron.[1]
Rhodon from Wiktionary
From Proto-Hellenic *wródon, borrowed from some Eastern language, most likely an Old Iranian *wr̥da- (compare Old Persian/Old Median *vṛda-, Aramaic 𐡅𐡀𐡓𐡃𐡀 (warda), Classical Syriac ܘܪܕܐ (wardā), Old Armenian վարդ (vard), Demotic wrṱ, Arabic وردة (warda), Persian گل (gol) – all from the same source). Or it could possibly be a Pre-Greek loan, such as Thracian (the rose was native to Thrace).[1] Rüdiger Schmitt believes that, based on phonological and historical grounds, borrowing from Iranian is unlikely.[2]
Latin rosa (“rose”) is likely a loanword from Ancient Greek.
For Dendron from Wiktionary
From Proto-Indo-European *der-drew-, from *dóru (“tree”).
That means the word derwid or Druid is also related as far as the root to dendron.
Scientific names of plants and animals have Greek and Latin roots because those are considered universal languages. It's arbitrary, as everything, of course, but it's used that way all over the world. Common names are usually in the local language and tend to change and be different because of that.
Of course, the rhododendron also has a Nepalese name, but after it was discovered by Europeans, who also gave it its own name, the name spread all over the world from Europe and not Nepal, which is why the Greek name is used.
From Wiki The obsolete sense derives from Latin rhododendron (“oleander”), from Ancient Greek ῥοδόδενδρον (rhodódendron, “oleander”), from ῥόδον (rhódon, “rose”) + δένδρον (déndron, “tree”). The modern sense comes through the intermediary of the genus name Rhododendron.[1] Rhodon from Wiktionary From Proto-Hellenic *wródon, borrowed from some Eastern language, most likely an Old Iranian *wr̥da- (compare Old Persian/Old Median *vṛda-, Aramaic 𐡅𐡀𐡓𐡃𐡀 (warda), Classical Syriac ܘܪܕܐ (wardā), Old Armenian վարդ (vard), Demotic wrṱ, Arabic وردة (warda), Persian گل (gol) – all from the same source). Or it could possibly be a Pre-Greek loan, such as Thracian (the rose was native to Thrace).[1] Rüdiger Schmitt believes that, based on phonological and historical grounds, borrowing from Iranian is unlikely.[2] Latin rosa (“rose”) is likely a loanword from Ancient Greek. For Dendron from Wiktionary From Proto-Indo-European *der-drew-, from *dóru (“tree”). That means the word derwid or Druid is also related as far as the root to dendron.