Add POT generation for ETR/ETRN() strings

extractable/Makefile

@@ -0,0 +1,44 @@
+# Makefile providing various facilities to manage translations
+
+TEMPLATE = runtime.pot
+MIN_COMPLETION = 0.20
+POFILES = $(wildcard *.po)
+LANGS = $(POFILES:%.po=%)
+
+all: update merge
+
+update:
+	@cd ../godot; python3 ../scripts/extract_extractable.py
+
+merge:
+	@for po in $(POFILES); do \
+	  echo -e "\nMerging $$po..."; \
+	  msgmerge -w 80 -C $$po $$po $(TEMPLATE) > "$$po".new; \
+	  mv -f "$$po".new $$po; \
+	  msgattrib --output-file=$$po --no-obsolete $$po; \
+	done
+
+check:
+	@for po in $(POFILES); do msgfmt -c $$po -o /dev/null; done
+
+# Export translation files with a high enough completion ratio.
+# Completion ratio is derived from statistics string such as:
+# 2775 translated messages, 272 fuzzy translations, 151 untranslated messages.
+# First number can be 0, second and third numbers are only present if non-zero.
+export:
+	@dest=../godot/editor/translations/extractable; \
+	mkdir -p $$dest; \
+	cp -f runtime_translations.gen.h $$dest/runtime_translations.gen.h; \
+	for po in $(POFILES); do \
+	  res=`msgfmt --statistics $$po -o /dev/null 2>&1 | sed 's/[^0-9,]*//g'`; \
+	  complete=`cut -d',' -f1 <<< $$res`; \
+	  fuzzy_or_untranslated=`cut -d',' -f2 <<< $$res`; \
+	  untranslated_maybe=`cut -d',' -f3 <<< $$res`; \
+	  if [ -z "$$fuzzy_or_untranslated" ]; then fuzzy_or_untranslated=0; fi; \
+	  if [ -z "$$untranslated_maybe" ]; then untranslated_maybe=0; fi; \
+	  incomplete=`expr $$fuzzy_or_untranslated + $$untranslated_maybe`; \
+	  if `awk "BEGIN {exit !($$complete / ($$complete + $$incomplete) > $(MIN_COMPLETION))}"`; then \
+	    echo $$po; \
+	    msgattrib -w 80 --translated --no-fuzzy --no-location $$po | sed -e "/^#\. .*/d" > $$dest/$$po; \
+	  fi; \
+	done;