Remove unused language keys from data/web/lang/lang.*.php

helper-scripts/check_translations.rb checks if keys present in the master
translation file are used in any php or js code.  Writes a sed comand to
stdout to remove unused keys from all lang files.

This saves unnecessary work when translating.

helper-scripts/check_translations.rb

@@ -0,0 +1,34 @@
+#!/usr/bin/ruby
+
+MASTER="en"
+
+DIR = "#{__dir__}/.."
+
+keys = %x[sed -r 's/.*(\\['.*'\\]\\['.*'\\]).*/\\1/g' #{DIR}/data/web/lang/lang.#{MASTER}.php | grep  '^\\\[' | sed 's/\\[/\\\\[/g' | sed 's/\\]/\\\\]/g'|sort | uniq]
+
+not_used_in_php = []
+keys.split("\n").each do |key|
+  %x[git grep "#{key}" -- #{DIR}/data/web/*.php #{DIR}/data/web/inc #{DIR}/data/web/modals]
+  if $?.exitstatus > 0
+    not_used_in_php << key
+  end
+end
+
+# \['user'\]\['username'\]
+# \['user'\]\['waiting'\]
+# \['warning'\]\['spam_alias_temp_error'\]
+
+not_used = []
+not_used_in_php.each do |string|
+  section = string.scan(/([a-z]+)/)[0][0]
+  key     = string.scan(/([a-z]+)/)[1][0]
+  %x[git grep lang.#{key} -- #{DIR}/data/web/js/#{section}.js]
+  if $?.exitstatus > 0
+    not_used << string
+  end
+end
+
+puts "# Remove unused translation keys:"
+not_used.each do |key|
+  puts "sed -i \"/\\$lang#{key}.*;/d\" data/web/lang/lang.??.php"
+end