most code editors can be used for JSON editing, but if you have large resource files or many locales you can probably better use a specialized tool, which keeps track of missing translations
BabelEdit is a very capable and affordable resource editor, for both JSON and java properties. It can edit JSON flavours for vue and angular libraries and also has support for other resource bundle formats. However it can not convert between formats. Only conversion between flat and nested JSON files is supported.
the Eclipse Resource Bundle Editor plugin is a FANTASTIC editor for eclipse: More info here https://essiembre.github.io/eclipse-rbe/
Attesoro is another free resource editor, a bit more limited and dated, but still usable.
BabelEdit is a very capable and affordable resource editor, for both JSON and java properties.
Below you can see some screenshots of the eclipse resource bundle editor plugin. I really recommend this tool.
INFO Make sure your files are all utf-8 encoding. It's also good i18n practice to liberally use cfprocessingdirective