Only building the packages is a global option. It therefore can't be used where the build list includes packages which will need to be installed as dependencies for other packages in the build list [for example tdesdk needs tdepim to be installed].
There is an override in the Misc SlackBuilds for non-trinity source archive URLs. Non-trinity builds have been included where a TDE package requires a dependency that is not in Slackware, or where it's an alternative to a TDE package.
i18n support [locale and html/help docs] in the packages is restricted to whatever is selected in the ./BUILD-TDE.sh 'Select Additional Languages' screen and, of that, to whatever is available in any individual package source.
Additionally for the development builds, translations for the .desktop files are determined from the LINGUAS variable which is set in this build shell to the additional languages selected.
Because of its position in the Slackbuild and the patch -p0 option, the path to the patched file must start with 'tde-i18n-{lang}' - see tde-i18n-en_GB-patch for an example.
The individual TDE apps can be cloned from Trinity git, so the build is set up to do that - except for individual language packs of tde-i18n. The whole tde-i18n download is ~1x10^6 bytes, so to reduce that, wget is used to download individual tde-i18n-$lang packs as they are not git repositories.
Once any git repository has been cloned, further downloads are updates only[2], giving the best options - only fetching what is needed, and incremental updates.
[2] The i18n downloads with wget can't be updated because cgit produces 'current time' timestamps. The consequence is that if tde-i18n-$lang is a part of the build after its initial download, it will be downloaded again. As updates are infrequent, once built, there will probably be no need to do so again and so tde-i18n for a particular language will probably only be run once. On that basis I don't see this being a significant issue.
[3] The Misc directory contains SlackBuilds for software that might already be installed from other sources. Please check because any misc builds selected here could overwrite them.
[4] The README for a native build for Raspberry Pi3 [[README-Raspberry-Pi3.md](./README-Raspberry-Pi3.md)] is now out-of-date and cross compiling is a better option.
[5] Building the kalzium equation solver needs ocaml and facile installed. They will be built, packaged, and installed during the tdeedu build if the source archives are pre-downloaded to the 'src' directory.