These replacements are default only for germans/austrians/swiss. I work mostly for hungarian clients. Hungarian alphabet shares some accented letters with german but we use different replacements in URL slugs (o for ö, u for ü). Symphony's slugger does a decent job if you don't interfere with it so my recommendation is to move everything from DEFAULT_REPLACERS constant to DE_REPLACERS (and keep DEFAULT_REPLACERS as an empty array if you want to maintain 100% backward compatibility).
These replacements are default only for germans/austrians/swiss. I work mostly for hungarian clients. Hungarian alphabet shares some accented letters with german but we use different replacements in URL slugs (o for ö, u for ü). Symphony's slugger does a decent job if you don't interfere with it so my recommendation is to move everything from DEFAULT_REPLACERS constant to DE_REPLACERS (and keep DEFAULT_REPLACERS as an empty array if you want to maintain 100% backward compatibility).