[Решено] language code change

Background of the issue:
Vendor webtoffee is working on translating packing slip and mentioned that our site is using language code he-IL (hyphen) instead of he_IL (underscore). When this was updated on the staging website staging6.jlmwines.com, it resolved a problem. We would like to test making this language code change and have backups, but want to be better informed before testing.

Symptoms:
Ongoing translation problems possibly due to incorrect language code format.

Questions:
Where is this setting language code changed?
Are the steps in the above article still correct?