Texts and labels are organised in language-specific include-files, such as this file for English. Basically you need to provide a file to me similar to this one, only in your language.
Each text or label has a unique ID; you need to translate the text which belongs to an ID. However, you need to understand the context of a text or label. In some cases that's not so easy as some labels are quite short. Therefore you can set your computer (or tablet, mobile) into a "translator mode" - this will store a cookie which tells the website to use a special language file. This special language file contains the labels with a specific ID, so you can identify the respective label. Download special language file.
The entire website will only show these specific labels in translator mode. Each specific label has a number so it's easier to find in the file. So this is what you have to do:

1. Download this generic special language file.
2. Enable translator mode on your device. Note that now the labels will be longer than the original text (in English); this my affect layout.
3. Open a text editor and replace the respective texts. So $lang['Share_Chat_ID'] = "{0001}Share Chat"; would become $lang['Share_Chat_ID'] = "Compartir chat"; for Spanish. Or $lang['All_entries_will_be_deletedlocal'] = "{0054}This chat will be deleted from this device. Other people with its access link can still see it. You can re-open it later with the correct link (e.g. from the QR code). To remove this chat completely for everyone, you need the administration PIN."; would become $lang['All_entries_will_be_deletedlocal'] = "Este chat se eliminará de este dispositivo. Otras personas con su enlace de acceso aún pueden verlo. Puede volver a abrirlo más tarde con el enlace correcto (por ejemplo, desde el código QR). Para eliminar este chat por completo para todos, necesita el PIN de administración.";
4. If you need to look up the texts for an already existing language, open the website in a different browser or on a different device. There the translator mode will not be enabled.
5. When you are done, email the file to me.
6. Note that the data privacy pages are not filled from the language files; for these I would just need the translated texts in plain text via email.
7. When ready, don't forget to switch back your site to normal mode.

When translating the labels and texts, please consider:

• When punctuation is needed, it's part of the text (e.g. a trailing dot or apostrophe).
• There are no leading or trailing spaces.
• In some cases a text on the screen consists of two fragments, e.g. "The chat with ID ... was not yet saved." - these are actually two labels, as a parameter (the actual chat ID) has to be added in the middle.
• In very rare cases the text contains HTML tags, e.g. "<b>Caution!</b>". Please include this HTML part.
• In some cases a text may not be visible directly, e.g. when it is displayed only on mouse hover. Contact me if you are looking for a text which should exist, but you do not find it. Some texts are used in the notification emails. It may also happen that a text is not used anymore at all; that should be very rare.
• If there is a distinction between formal and informal speech in your language (as e.g. in German): The general tone is rather informal.
• Please do NOT use double quotes (") in a text, only single quotes (').
• The entire website is UTF-8 encoded, so also special characters or non-Latin languages should not be a problem.
• Please try to more or less keep the length of the original texts, otherwise the layout may be affected.

I really appreciate your help! Contact me in case of questions!