Add a tool to verify language files are well formed

I'm not going to pretend this is a beautiful script, but it's good
enough for basic validation of language files.

tools/language.lua

@@ -0,0 +1,111 @@
+--- Rewrites language files in order to be consistent with en_us.
+--
+-- This will take every given language file and rewrite it to be in the same
+-- order as the en_us file. Any keys which appear in the given file, but not
+-- in en_us are warned about.
+--
+-- When passing the `-v` flag, we also print any missing commands.
+--
+-- Note, this is not intended to be a fool-proof tool, rather a quick way to
+-- ensure language files are mostly correct.
+--
+-- @example
+--
+--     # Reformat all files
+--     > lua tools/language.lua
+--     # Reformat German, and warn about missing entries
+--     > lua tools/language.lua -v de_de
+
+local primary = "en_us"
+
+local secondary = {
+    "de_de",
+    "fr_fr",
+    "it_it",
+    "pt_br",
+    "sv_se",
+}
+
+local verbose = false
+
+local path = "src/main/resources/assets/computercraft/lang/%s.lang"
+
+
+local args = {...}
+for i = #args, 1, -1 do
+    if args[i] == "-v" or args[i] == "--verbose" then
+        table.remove(args, i)
+        verbose = true
+    end
+end
+if #args > 0 then secondary = args end
+
+-- Read the contents of the primary language file
+local primary_contents, n = {}, 1
+for line in io.lines(path:format(primary)) do
+    local key = line:match("^([^=]+)=.*$")
+    if key then
+        primary_contents[n], n = key, n + 1
+    elseif line == "" or line:sub(1, 1) == "#" then
+        primary_contents[n], n = line, n + 1
+    else
+        io.stderr:write(("Unknown line %q in %s\n"):format(line, primary))
+        os.exit(1)
+    end
+end
+
+for _, language in ipairs(secondary) do
+    local keys = {}
+
+    for line in io.lines(path:format(language)) do
+        local key, value = line:match("^([^=]+)=(.*)$")
+        if key then
+            if keys[key] then
+                io.stderr:write(("Duplicate keys for %q in %q\n"):format(key, language))
+                os.exit(10)
+            end
+
+            keys[key] = value
+        elseif line ~= "" and line:sub(1, 1) ~= "#" then
+            io.stderr:write(("Unknown line %q in %s\n"):format(line, language))
+            os.exit(1)
+        end
+    end
+
+    local h = io.open(path:format(language), "wb")
+    local previous_blank = flase
+    for _, line in ipairs(primary_contents) do
+        if line == "" then
+            if not previous_blank then
+                previous_blank = true
+                h:write("\n")
+            end
+        elseif line:sub(1, 1) == "#" then
+            h:write(line .. "\n")
+            previous_blank = false
+        else
+            local translated = keys[line]
+            if translated then
+                h:write(("%s=%s\n"):format(line, translated))
+                keys[line] = nil
+                previous_blank = false
+            elseif verbose then
+                io.stderr:write(("Missing translation %q for %q\n"):format(line, language))
+            end
+        end
+    end
+
+    if next(keys) ~= nil then
+        local extra = {}
+        for k, v in pairs(keys) do extra[#extra + 1] = ("%s=%s\n"):format(k, v) end
+        table.sort(extra)
+
+        io.stderr:write(("%d additional unknown translation keys or %q\n"):format(#extra, language))
+
+        if not previous_blank then h:write("\n") end
+        h:write("#Unknown translations\n")
+        for _, line in ipairs(extra) do h:write(line) end
+    end
+
+    h:close()
+end