duplicate i18n key breaks i18n in packaged build only

[mifi]

Initial checklist

• I understand this is a bug report and questions should be posted in the Community Forum
• I searched issues and couldn’t find anything (or linked relevant results below)

Link to runnable example

No response

Steps to reproduce

create a new Uppy plugin and use the same i18n key as an existing plugin. e.g. @uppy/google-drive-picker using pluginNameGoogleDrive in the UI

i've worked around it with aa02fe2 but it should be fixed in the build scripts so that we don't have to waste more time on this

Expected behavior

The value of key pluginNameGoogleDrive should be presented

Actual behavior

the literal string pluginNameGoogleDrive gets presented. note that I'm not 100% sure that this is the cause of the issue, but we will see after #5619 is merged