I'm a big fan of extensive reading apps for language learning, and even collaborated on such an app some 10 years ago. It eventually had to be shut down, sadly enough.
Right now, the biggest one in the market is the paywalled LingQ, which is pretty good, but well, requires money.
There's also the OG programs, LWT (Learning With Texts) and FLTR (Foreign Language Text Reader), which are so cumbersome to set up and use that I'm not going to bother with them.
I presently use Vocab Tracker as my daily driver, but I took a spin around GitHub to see what fresh new stuff is being developed. Here's an overview of what I found, as well as VT itself.
(There were a few more, like Aprelendo and TextLingo, which did not have end-user-friendly installations, so I'm not counting them).
Vocab Tracker
++ Available on web ++ 1-5 word-marking hotkeys and instant meanings makes using it a breeze ++ Supports websites
-- Default meaning/translation is not always reliable -- No custom languages -- Ugliest interface by far -- Does not always recognise user-selected phrases -- Virtually unusable on mobile -- Most likely no longer maintained/developed
Lute
++ Supports virtually all languages (custom language support), including Hindi and Sanskrit ++ Per-language, customisable dictionary settings ++ Excellent, customisable hotkey support
-- No instant meaning look-up makes it cumbersome to use, as you have to load an external dictionary for each word -- Docker installation
LinguaCafe
++ Instant meanings thanks to pre-loaded dictionaries ++ Supports ebooks, YouTube, subtitles, and websites ++ Customisable fonts ++ Best interface of the bunch
== Has 7 word learning levels, which may be too many for some
-- Hotkeys are not customisable (yet) and existing ones are a bit cumbersome (0 for known, for eg.) -- No online dictionary look-up other than DeepL, which requires an API key (not an intuitive process) -- No custom languages -- Supports a maximum of 15,000 characters per "chapter", making organising longer texts cumbersome -- Docker installation
Dzelda
++ Supports pdf and epub ++ Available on web
-- Requires confirming meaning for each word to mark that word, making it less efficient to read through -- No custom languages, supports only some Latin-script languages -- No user-customisable dictionaries (has a Google Form to suggest more dictionaries)
