I recently noticed in גמ' מגילה כא עמוד ב a possibility that there was some point where Targum accompanied the public recitation of the Hallel, due to the line:
"ובהלל ובמגילה אפילו עשרה קורין ועשרה מתרגמין"
Rashi there does not include מתרגמין in the girsa but Tosafos and other rishonim still include it.
There is also the possibility that "קורין" refers to both Hallel and Megilla while "מתרגמין" would only apply to Megilla (less unusual as we normally associate the old practice of a meturgeman with a public reading from a written Hebrew portion of כתבי הקודש).
While the Rambam makes no mention of Targum for Hallel, in הל' מגילה וחנוכה ג:יב-יד, the way he presents the original way of reciting Hallel in shul is a responsive interaction between shliach tzibbur and kehilla which makes it easier to imagine how a Targum might have possibly fit in.
Does anyone out there know of a place or time where a there was an actual minhag to translate a recitation of Hallel to Aramaic (or even merely sources which discuss this)?