Add translator comments to every string that contains a placeholder

[johnbillion]

Strings that contain placeholders — such as %s, %d, and %1$s — should include accompanying translator comments. This provides context to translators and allows for more accurate translations.

The meaning of even seemingly simple strings containing placeholders may not be clear to translators who are not intimately familiar with WordPress, unless a translator comment is provided.

[ramiy]

+1

[johnbillion]

In 39323:

I18n: Begin introducing translator comments for strings which include placeholders but no accompanying translator comment.

Adds context to one string used in two different contexts for the new user and new site signup email notification.

More to come.

See #38882

[johnbillion]

In 39324:

Remove an erroneous @TODO introduced in [39323].

See #38882

[johnbillion]

In 39326:

I18n: Introduce more translator comments for strings that contain placeholders but don't have an accompanying translator comment.

See #38882

[ocean90]

@johnbillion Comments which are for the placeholders %s or %d shouldn't use "1", it should be the name of the placeholder.

[desrosj]

@johnbillion Are you able to wrap this up or summarize what is left? Also, it appears that @ocean90's concern still needs to be addressed.

[Presskopp]

related #44360

[johnbillion]

Superseded by #44360.