Internationalize the user interface

[MarkEWaite]

Internationalize the user interface to allow Crowdin translation

Many of the plugin strings were internationalized references from the Java, Jelly, and Groovy source code using the form:

${%Internationalized string}

That form of reference does not require an entry in the English language properties file. Unfortunately, without an entry in the English language properties file, Crowdin does not find the source string to be used as a basis for translation.

This pull request converts from the previous form into:

${Internationalized_string_reference}

The property file is created with the internationalized string reference symbol and the internationalized string, like this:

Internationalized_string_reference=Internationalized string

That provides an English language source string, "Internationalized string" that Crowdin will detect and offer for translators and proofreaders.

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