reftex-translate-to-ascii-function

reftex-translate-to-ascii-function is a variable defined in `reftex-vars.el'.
Its value is

reftex-latin1-to-ascii

• This variable may be risky if used as a file-local variable.

Documentation:
Filter function to convert a string to ASCII.
The function is used to process a context string before it is
used to derive a label from it. The intended application is to
convert ISO or Mule characters into something valid in labels.
The default function removes the accents from Latin-1 characters.
X-Symbol (>=2.6) sets this variable to the much more general
`x-symbol-translate-to-ascii'.

You can customize this variable.