[espeak-ng:master] New Comment on Issue #854 Some French diacritics are explicitly spelled out
By CorentinJ:

Yes I had found the same problem with ô indeed.

Should we only worry about letters which can be words? The issue also persists with other diacritics such as é, è, ê, â, ..., but I suppose they won't pop up as single character words in sentences.

[espeak-ng:master] New Comment on Issue #854 Some French diacritics are explicitly spelled out
By valdisvi:

If letter can be also word, it should be noted with _ prefix in xx_list file. For other possible problematic letters look at fr_list file.