Note: I am not disputing how the English translations translate Τετέλεσται, but pointing out the secondary meaning of the word Jesus probably used.
The Hebrew word that Τετέλεσται (it is finished) best translates is שָׁלֵם, which is how the Syriac Peshitta* and modern Hebrew** translations translate Τετέλεσται in John 19:30.

While שָׁלֵם in the context of translating Τετέλεσται in John 19:30 has the meaning, “It is finished,” שָׁלֵם in the Torah has the meaning to make restitution. Thus, in the Jewish mind this word also brings up the thought of to pay or make restitution, to restore or make peace, to make whole.

The fact is Jesus’ words having a secondary meaning often more important than the primary is not foreign in the Gospel of John. Here Jesus’ own words seem to point his disciples to Jesus’ sacrificial death and atonement. Thus, this method of looking for the historic Jesus using Jesus’ words points to the same Jesus portrayed in the New Testament.
[Charts made with Logos Bible Software 8.]
See also In John 20:17 does Jesus intent ἀναβέβηκα to have a secondary meaning related to sacrifice?
- ܡܫܰܠܱܡ (shlm) in Kiraz, G. A. (Ed.). (2002). The Peshitta (Jn 19:30). Bellingham, WA: Logos Bible Software. [5th century]
**
נִשְׁלַם in ha-Berit ha-ḥadashah. (2000). (Jn 19:30). Israel: The Bible Society in Israel.
**
נִשְׁלָם in Franz Julius Delitzsch [1813-1890]. (n.d.). Delitzsch Hebrew New Testament (Jn 19:30).