I read your post "Starting localization to interlingua (ia) language" on mozilla.dev.l10n.new-locales where you asked to help you to get started in translating Firefox to Interlingua.
You can translate in two different ways:
1. Online on the Mozilla servers
2. Offline at home.
The first way has the advantage that you need translate only - you must not care about creating the language pack and you will have even complete builds for Windows 32, Windows 64, Linux 32, Linux 64 and Mac
in your language. The l10n drivers will do that for you. The translation is done in the Aurora phase of every new version, that's the alpha version. Normally you have 6 or 7 weeks for translating. Then the Aurora version will become beta and you can translate for the next Firefox version in Aurora. Currently Firefox 49 is translated in Aurora, on August 2 it will become beta and Firefox 50 will be translated in Aurora then. But don't be afraid - you won't be pressed for time, take the time you need.
You can translate on two platforms:
The current Firefox 49 covers 46.119 words resp. 10.550 strings. So it will be a lot of work for you if you have to do it alone. But it is possible, I translate alone as well, even into two languages and not only for Firefox for desktop. There will be very much work at the very beginning - when you will translate the next version you need translate new or changed strings only.
If you want to translate online you should ask l10drivers to add Interlingua (ia) to Pootle or Pontoon. Besides there are some localization requirements you will be asked by the l10n drivers. If you want to collaborate with the team of your greatest competitor - Esperanto - ;-) you should translate on Pontoon if you decide to localize online.
Every month nine alpha versions (so-called nightlies) will be released - the current nightly is 49.0a2. Usually there are no changes in the number or text of the strings to be translated in Aurora. You can download the current Aurora build and test your language pack. The language pack is built by the l10n drivers - so you don't care about it. Simply download both the Firefox Aurora build (currently 49.0a2) and the related language pack.
You can translate offline as well of course. But you will have more work. You need also a current Aurora build (49.0a2) and an existing example language pack in another language - in English or in another language.
Mozilla uses .dtd and .properties files. As character encoding you should use UTF-8 without BOM. Additional to the Firefox Aurora build and the example language pack you need a text editor that supports Unicode. Besides I recommend a Diff program you will need when you create the language pack for the next Firefox version to find new, changed, and obsolete strings.
A language pack has the file extension .xpi. It is, actually, an installable zip file, so you need a zip program as well to unpack the example language pack and to pack your new language pack. There are two important files inside a language pack: "install.rdf" which controls the installation of the language pack and "chrome.manifest" where you have to register your "ia" locale. They are text files.
Finally you should download an extension to switch to your locale in Firefox. You could use:
- Locale Switcher. https://addons.mozilla.org/ru/firefox/addon/locale-switcher/
- Simple Locale Switcher: https://addons.mozilla.org/ru/firefox/addon/simple-locale-switcher/
- Zing Locale Switcher: https://addons.mozilla.org/ru/firefox/addon/zing-locale-switcher/
The most simple one is Locale Switcher. Install it from addons.mozilla.org by clicking the "Add to Firefox" button and then your language pack in Firefox. Locale Switcher creates menu items in the Tools menu for each language. You will see the menu item "ia" then. Choose it and restart Firefox and your Firefox should be in Interlingua then. But, currently, this is still future, isn't it? :-)
If you have still questions about something, send me an email.