Thank you Rob.
Yes, the demo "works" on my machine to (also running perl 5.26) in that sense that both icons and labels are displayed. The point of my question was to have the labelled translated (in my case in French). Interestingly, you mention that the translation should happen automatically based on the computer's local settings. If you can confirm that, this would mean that I may need to investigate my gtk install rather than my perl code, which was actually an alternative I had in mind too.
So could you please confirm that the translation should be triggered automatically via the computer settings (have you observed it)? This would help me moving forward.