SubTranslate/SubTranslate.lua

-- Options
local o = {
    source_lang = 'en', -- Translate from, e.g. 'ru', 'en', 'de', etc. Change to 'auto' to detect the source language
    destination_lang = 'ru', -- Translate to
    duration = 10, -- how long will the translation be shown on the OSD screen (in secs.)
    key_binding = "t" -- Keybind for translating the current sub 
}

local mp    = require 'mp'
local utils = require 'mp.utils'

-- Custom URL-encode function (Lua 5.1+)
local function url_encode(str)
    if not str then return "" end
    -- Convert line breaks to spaces, trim leading/trailing whitespace
    str = str:gsub("\n", " "):gsub("^%s*(.-)%s*$", "%1")
    -- Percent-encode special characters
    str = str:gsub("([^%w _%%%-%.~])", function(char)
        return string.format("%%%02X", string.byte(char))
    end)
    -- Replace spaces with %20
    str = str:gsub(" ", "%%20")
    return str
end

local function translate_subtitle()
    -- Get the current subtitle text
    local text = mp.get_property("sub-text")
    if not text or text == "" then
        mp.osd_message("No subtitles to translate.")
        return
    end

    -- Encode text for URL
    local encodedText = url_encode(text)

    -- Google Translate API endpoint
    local url = string.format(
        "https://translate.googleapis.com/translate_a/single?client=gtx&sl=" .. o.source_lang .. "&tl=" .. o.destination_lang .. "&dt=t&q=%s",
        encodedText
    )

    -- Use curl to fetch the translation result
    local res = utils.subprocess({
        args = {"curl", "-s", url},
        cancellable = false
    })

    if res.status ~= 0 or not res.stdout or res.stdout == "" then
        mp.osd_message("Translation request failed.")
        return
    end

    -- Parse the JSON returned by Google Translate
    local data = utils.parse_json(res.stdout)
    if not data or not data[1] then
        mp.osd_message("Failed to parse translation.")
        return
    end

    -- Concatenate translation chunks
    -- Google may split the translation into multiple segments for punctuation, etc.
    local translation_parts = {}
    for _, segment in ipairs(data[1]) do
        if segment and segment[1] then
            table.insert(translation_parts, segment[1])
        end
    end
    local translation = table.concat(translation_parts, "")

    mp.osd_message(translation, o.duration)
end

-- Bind the function to a hotkey, e.g. Ctrl+T
mp.add_key_binding(o.key_binding, "translate_subtitle", translate_subtitle)