Normally the language for the spellcheck dictionary will be set by the system locale of your workstation. For example, if you are in Sydney the default language for the dictionary will be English.
However, if your project is using the RippleDown Translator, then the language for the spellcheck dictionary will be set by the translation that is currently selected.
If the default language for the dictionary is not what you want, then you can select another language.
When you select the language for the dictionary, this setting will only apply to your user account, that is, not to other RippleDown users.