This thread is resolved. Here is a description of the problem and solution.
Problem: adding 2 different logos images and translating them via String Translation doesn't work.
Solution: the client added a snippet directly in the child theme's template. See link below
Relevant Documentation: https://wpml.org/forums/topic/trying-to-use-different-logos-for-each-language/#post-4329725
This is the technical support forum for WPML - the multilingual WordPress plugin.