Experience Applying Language Pack after go live?

Summary

Are there any risks in applying the language pack if you are already live?

Content

Hello, We went live on Financials(GL,AR, AP, FA), SCM(PO) and Project Financials in July of 2018 for the US.  We are now expanding to Canada and Latin America.  Even though the implementation was intended to be global the language pack was not applied as part of wave 1(US).  We are preparing to apply as part of wave 2 to handle Canadian French and Latin America: Spanish and Portuguese.   We are bring told that the language pack must be applied to all instances simultaneously versus applying only to a dev and test environment, validating and then moving to production?   This seems