Hi @chengjianping,
- First please make a back-up of your site. We always recommend doing a backup when you are working with the database.
All translations are saved in *trp dictionary_ and *trp_gettext tables from your database. For example, in my case, if I want to delete the Spanish additional language from my site, I need to delete the ce3_trp_dictionary_en_gb_es_es table and ce3_trp_gettext_es_es tables.
Regarding slugs, post, and term slugs have the translations in _postmeta and _termmeta tables.
Taxonomy and CPT slugs have the translations in wp_options. The names of the options are trp_taxonomy_slug_translation and trp_post_type_base_slug_translation.
Please note that the information I provided above is useful if you already have translated content for those languages. If you don’t have any translated content, you can simply remove the language in TranslatePress by going to Settings > General.
2. Yes, for example, for the UK and the United States, you would have English (UK) and English (United States)
3. For additional languages, the URL will always include the suffix for the language the user is accessing.
For the default language, you need to enable the ‘Use a subdirectory for the default language’ setting in TranslatePress under Settings > General. This will change the URL for the default language to yourwebsite.com/en.