JLabeledChoice isn't localized (L10N)

@milamberspace ([Bug 59131](https://bz.apache.org/bugzilla//show_bug.cgi?id=59131&redirect=false)):
The new change of the Method field to have an editable field to add or delete a method bring an issue in the localized versions of JMeter, the label of Add and Delete button isn't localize, it's hard-coded in the src/jorphan/org/apache/jorphan/gui/JLabeledChoice.java L149/L153.

This class is build inside the jorphan.jar package, which don't have any import form JMeter API, so it's not possible to use the JMeter L10N mechanism.

Three options:

1/ Change the "Add" and "Del" label with " + " and " - " characters. Not necessary to add some L10N mechanism, the plus and minus are recognized for Add and Delete action in UI.

2/ Use icons for + and - (same than the collapse/expand toolbar button). Need to add inside the jorphan.jar the icons and manage the HiDPI (some properties to add or try to manage this automatically)

3/ Add some L10N messages.properties mechanism inside the jorphan.jar and use this to translate the UI.

In attachment, some draft screenshot.

What is your prefer option ? 1 / 2 / 3 / other way ?

Created attachment [JLabeledChoice_Not_L10N.png](https://apache.github.io/jmeter-bugzilla-attachments/31/59131/33630/JLabeledChoice_Not_L10N.png): JLabeledChoice Not L10N

Version: Nightly
OS: All

Depends on:
* https://github.com/apache/jmeter/issues/3863