To consistently obtain correct results when capitalizing / decapitalizing locale insensitive strings (such as programming language identifiers), Locale.ROOT must be specified as a parameter to String.toUpperCase() and String.toLowerCase(). This blog: https://mattryall.net/blog/the-infamous-turkish-locale-bug summarizes the problem with allowing the default locale to be used with String.toUpperCase() and String.toLowerCase(). Also see the note in the Javadoc here: https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html#toUpperCase() which promotes the usage of Locale.ROOT for capitalizing locale independent strings. A user with a Turkish locale will see surprising and incorrect results with capitalizing the letter "i". The capitalization rules for other locales may also produce incorrect results.