public static class L10n

Use this class to localize your text shown in the Unity Editor. You need a po file (ja.po for example) and an asmdef (Assembly Definition) file. Add this syntax to define the LocalizationAttribute in any script in the assembly: [assembly:UnityEditor.Localization].

Place all po files within the asmdef folder. Additional Resources: https://docs.unity3d.com/Manual/assembly-definition-files.html

Unity looks up each translation in a localization group. The methods that take a group name use that group directly. The methods that take no group name identify the assembly that called them, and use the group named by the LocalizationAttribute on that assembly.

Note: On the CoreCLR scripting backend, Unity can't reliably identify the calling assembly, because the JIT compiler can inline the caller and remove its stack frame. Pass an explicit group name to avoid this.