Why Java Character.toUpperCase/toLowerCase has no Locale parameter like String.toUpperCase/toLowerCase

As the Javadoc says:

In general, String.toUpperCase() should be used to map characters to uppercase. String case mapping methods have several benefits over Character case mapping methods. String case mapping methods can perform locale-sensitive mappings, context-sensitive mappings, and 1:M character mappings, whereas the Character case mapping methods cannot.

So use String.toUppercase()

From the Character#toUpperCase(int) Javadoc,

In general, String.toUpperCase() should be used to map characters to uppercase. String case mapping methods have several benefits over Character case mapping methods. String case mapping methods can perform locale-sensitive mappings, context-sensitive mappings, and 1:M character mappings, whereas the Character case mapping methods cannot.

So, the answer is your second example (String.toUpperCase)