We're using [a-z] ranges with sed and grep, and POSIX does not specify
their behaviour in non-ASCII locales:

  In the POSIX locale, a range expression represents the set of
  collating elements that fall between two elements in the collation
  sequence, inclusive. In other locales, a range expression has
  unspecified behavior
    -- IEEE Std 1003.1-2017, § 9.3.5 (7)

This can lead to no results, or invalid replacements, which in turn can
lead to broken builds or broken build artifacts.

Fixes: #1662