develop syntax uses {…}, but the broader software ecosystem seems to have settled on a paradigm in which interpolated parts of text are indicated by either ${…} (JavaScript template literals and Mako templates) or {{…}} (Mustache, Jinja(2) and Angular).

Unless there is a clear pre-existing convention for single braces within the context of internationalization, I think it would be wise to conform with that external paradigm rather than diverging from it.