There are two duplicate issues related to this #2506427: [meta] !placeholder ...

There are two duplicate issues related to this #2506427: [meta] !placeholder causes strings to be escaped and makes the sanitization API harder to understand and #2506445: Replace !placeholder with @placeholder in t() and format_string() for non-URLs in tests. Most work has been done in #2506445: Replace !placeholder with @placeholder in t() and format_string() for non-URLs in tests, we should continue work on that issue and close the others.