Use literal 'wp-auth0' rather than WPA0_LANG constant

[idpaterson]

Translation tools are generally not able to map a runtime constant like WPA0_LANG to a value for the text domain and therefore most of the text within this plugin was not automatically available for translating. A literal string value for the text domain ensures better compatibility.

This pull request updates all occurrences of WPA0_LANG to the literal 'wp-auth0' and adds the text domain in a few places where it was missing. The literal value uses either single or double quotes for consistency with the adjacent translated text. The WPA0_LANG constant is still defined to avoid backwards compatibility issues for anything that may still use it.

This problem was discovered when working on #308. I attempted to use the popular Loco translation plugin to change the error message text but only a few strings (those with the default text domain) were available for translation. I was able to use * as a wildcard in Loco but then the particular error message that I needed to change was not translatable (see #312).

[cocojoe]

Can you fix conflicts please, also why doesn't a constant work?

[idpaterson]

WordPress strongly suggests against it because gettext which parses these files does not interpret PHP. It knows how to pull out a literal text domain but cannot map a variable or constant to the corresponding value, so you end up with an incorrect or missing text domain that inhibits translation.

Thanks for taking a look, I will fix up the conflicts.

[cocojoe]

Ah good thanks for the reference.

[idpaterson]

It seems this once again has conflicts; I'm not inclined to continue fixing conflicts for every minor typo fix that is committed. Please let me know whether this will actually be merged.

[cocojoe]

Sorry about this @glena any feelings against this? seems to be the preferred method.

[cocojoe]

@idpaterson Can you rebase to master and fix conflicts thanks.

[idpaterson]

I am happy to rebase and fix the conflicts if this is en route to acceptance but will wait until you've all agreed that this is an acceptable change.

[cocojoe]

This should be fine, please rebase 😄

[idpaterson]

This should be good to go, note that there are both text domains switched from the WPA0_LANG constant and newly added text domains that were previously blank. There are also a few alternate domains (wp_auth0_widget_domain, wpb_widget_domain) that were not modified.

[cocojoe]

So this looks fine, I was a little hesistant on this however it is the preferred method from the WP docs. Although I am unsure how PHP processes a define vs a variable. @glena any thoughts here?

[cocojoe]

Oh, sorry @idpaterson can you rebase to dev please, same goes for your other PR Thx. So close 😄

[idpaterson]

Rebased this and #312 back to dev

[cocojoe]

Still think it's odd in some ways. However, is the WP preferred way and you also ran into issues with it so no harm in doing so. Any concerns @glena ? The define is still there in case something somewhere in the shadows references it 😄

[glena]

LGTM