There are two sides to this:

First—and more importantly—a professional translator’s interface is list of strings and some supplementary materials in, list of strings out. (Protip: given baseline i18n competence like not concatenating sencences out of parts, the quality of the translation you get is largely determined by the supplementary materials; screenshot every part of your UI and your translator will be willing to kiss you.) Both in communicating with clients and on the fast path of their own work (in CAT software like Across, Trados, etc.).

They do not need to see the code that fills in any placeholders, nor do they want to spend time and attention preserving it exactly as it’s been written—they just want to reorder the placeholders as the syntax of the language dictates. Arguably even %s vs %d is too much information. The ideal is {name} and {count}, and {1} and {2} are acceptable.

(By contrast, a very common issue is that like half of the sentence may need to change depending on the numeric value filled in for {count}, and two variants in English may map to anywhere between one and four after localization[1]. Template strings help with this not at all.)

Second—though this may be easier to fix—the two major ways to retrieve localized messages at runtime are integers in, strings out (most commercial tools out there) and strings in, strings out (GNU gettext), where the output strings are retrieved from some sort of data file that’s intentionally incapable of containing executable code (resource-only “MUI” DLLs, hashtables in GNU “MO”s, plain old text in Java “properties”, various kinds of XML, etc.).

Operating on pure data isn’t a strict necessity. It’s is largely a concession to the development process, which may not permit the string tables to go out to the localization contractors until principal QA is finished. The last thing you want is to insert engineering into the already-slow loop between the translators, the editors (or a translation agency employing both), and localization QA (hopefully in-house, using the actual live software to check the translations in context).

[1] https://www.gnu.org/software/gettext/manual/html_node/Plural...