Should I use t() in hook_update_N() or admin UI in a custom module?
Ever hear the expression &quot;You Play Like You Practice&quot;? If you get in the habit of NOT using t() for strings that are translatable just because it's only for your site (&quot;practice&quot;), then when it counts (i.e. &quot;play&quot;) you will probably also leave out t(), because that's what you're used to.
There is really no downside to doing it correctly here. You're not saving anything or making any measurable difference in performance. The upside is that if you do it the same everywhere, you're not going to introduce a bug by leaving off t() where it is needed, and you can then also use the automated coding standards tools to check your code without seeing a lot of fails from your missing t() functions - that keeps these many fails from obscuring the few real problems you might have.