#5183 Add locale strings for legends in forms

[thinkbulecount2]

From this issue: pkp/pkp-lib#5183

[NateWr]

Looks good. I left a few comments. In addition, let's move the new locale keys into pkp-lib. They can go into common.po.

With that change, you shouldn't need any PRs for OMP or OPS. But go ahead and test the pkp-lib changes in OMP and OPS just to make sure.

[thinkbulecount2]

cc: @NateWr

[thinkbulecount2]

Made changes, @NateWr.

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