> Is that what you mean?

Yes. (except for verb names.)

Mozilla localizers are familiar with ".properties" format.
If using ".properties", there is "English.properties" file and this makes easy to start localize.
I think that it isn't needed any spaces in the key.

For external command feeds, define them within the command like this?
CmdUtils.CreateCommand({
...
messages: {
execute.hello: [en: "Hello!", ja:"こんにちは！"],
preview.hello: [en: "Hello!", ja:"こんにちは！"]
}
});