[I18n] tooling and process

Before:

* Translations were imported from Crowdin via Gitea
* New strings were added by Forgejo in feature branches but never translated
* The build/merge-forgejo-locales.go script in the forgejo-i18n branch
  added/replaced Forgejo specific strings in the translated files at
  build time
* Conflicts arising from Gitea changes in locale_en-US.ini were resolved by moving around
  Forgejo strings

Transition:

* The build/merge-forgejo-locales.go is run once on the source
* The result is commited to the forgejo-development branch

After:

* Translation are exported and imported from translate.codeberg.org
* build/crowdin-to-weblate.sh run is run when rebasing (soft-fork)
  or cherry-picking (hard-fork) to collect new translations from
  Crowdin via Gitea
* In case of a conflict Forgejo translations are authoritative
* In the absence of a conflict Crowdin translations are uploaded to Weblate

(cherry picked from commit 9b5b714048)

build/crowdin-to-weblate.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+# Copyright 2024 The Forgejo Authors
+# SPDX-License-Identifier: MIT
+
+D=/tmp/crowdin-to-weblate
+mkdir -p $D
+
+function checkout() {
+    if test -d $D/gitea ; then
+        git -C $D/gitea reset --hard
+        return
+    fi
+
+    git clone --depth 1 https://github.com/go-gitea/gitea $D/gitea
+}
+
+function replace() {
+    go run build/merge-forgejo-locales.go $D/gitea/options/locale
+    cp -a $D/gitea/options/locale/* options/locale
+}
+
+function run() {
+    checkout
+    replace
+}
+
+"$@"

build/merge-forgejo-locales.go

@@ -0,0 +1,109 @@
+// Copyright 2022 The Forgejo Authors c/o Codeberg e.V.. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+//go:build ignore
+
+package main
+
+import (
+	"bufio"
+	"log"
+	"os"
+	"regexp"
+	"strings"
+)
+
+const (
+	trimPrefix   = "gitea_"
+	sourceFolder = "options/locales/"
+)
+
+// returns list of locales, still containing the file extension!
+func generate_locale_list() []string {
+	localeFiles, _ := os.ReadDir(sourceFolder)
+	locales := []string{}
+	for _, localeFile := range localeFiles {
+		if !localeFile.IsDir() && strings.HasPrefix(localeFile.Name(), trimPrefix) {
+			locales = append(locales, strings.TrimPrefix(localeFile.Name(), trimPrefix))
+		}
+	}
+	return locales
+}
+
+// replace all occurrences of Gitea with Forgejo
+func renameGiteaForgejo(filename string) []byte {
+	file, err := os.Open(filename)
+	if err != nil {
+		panic(err)
+	}
+
+	replacements := []string{
+		"Gitea", "Forgejo",
+		"https://docs.gitea.com/installation/install-from-binary", "https://forgejo.org/download/#installation-from-binary",
+		"https://github.com/go-gitea/gitea/tree/master/docker", "https://forgejo.org/download/#container-image",
+		"https://docs.gitea.com/installation/install-from-package", "https://forgejo.org/download",
+		"https://code.gitea.io/gitea", "https://forgejo.org/download",
+		"code.gitea.io/gitea", "Forgejo",
+		`<a href="https://github.com/go-gitea/gitea/issues" target="_blank">GitHub</a>`, `<a href="https://codeberg.org/forgejo/forgejo/issues" target="_blank">Codeberg</a>`,
+		"https://github.com/go-gitea/gitea", "https://codeberg.org/forgejo/forgejo",
+		"https://blog.gitea.io", "https://forgejo.org/news",
+		"https://docs.gitea.com/usage/protected-tags", "https://forgejo.org/docs/latest/user/protection/#protected-tags",
+		"https://docs.gitea.com/usage/webhooks", "https://forgejo.org/docs/latest/user/webhooks/",
+	}
+	replacer := strings.NewReplacer(replacements...)
+	replaced := make(map[string]bool, len(replacements)/2)
+	count_replaced := func(original string) {
+		for i := 0; i < len(replacements); i += 2 {
+			if strings.Contains(original, replacements[i]) {
+				replaced[replacements[i]] = true
+			}
+		}
+	}
+
+	out := make([]byte, 0, 1024)
+	scanner := bufio.NewScanner(file)
+	scanner.Split(bufio.ScanLines)
+	for scanner.Scan() {
+		line := scanner.Text()
+
+		if strings.HasPrefix(line, "license_desc=") {
+			line = strings.Replace(line, "GitHub", "Forgejo", 1)
+		}
+
+		if strings.HasPrefix(line, "[") && strings.HasSuffix(line, "]") {
+			out = append(out, []byte(line+"\n")...)
+		} else if strings.HasPrefix(line, "settings.web_hook_name_gitea") {
+			out = append(out, []byte(line+"\n")...)
+			out = append(out, []byte("settings.web_hook_name_forgejo = Forgejo\n")...)
+		} else if strings.HasPrefix(line, "migrate.gitea.description") {
+			re := regexp.MustCompile(`(.*Gitea)`)
+			out = append(out, []byte(re.ReplaceAllString(line, "${1}/Forgejo")+"\n")...)
+		} else {
+			count_replaced(line)
+			out = append(out, []byte(replacer.Replace(line)+"\n")...)
+		}
+	}
+	file.Close()
+	if strings.HasSuffix(filename, "gitea_en-US.ini") {
+		for i := 0; i < len(replacements); i += 2 {
+			if replaced[replacements[i]] == false {
+				log.Fatalf("%s was never used to replace something in %s, it is obsolete and must be updated", replacements[i], filename)
+			}
+		}
+	}
+	return out
+}
+
+func main() {
+	d := os.Args[1]
+	files, err := os.ReadDir(d)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	for _, f := range files {
+		p := d + "/" + f.Name()
+		os.WriteFile(p, renameGiteaForgejo(p), 0o644)
+	}
+}