py.mk: allow translation to be overriden in GNUmakefile

I like to use local makefile overrides, in the file GNUmakefile
(or, on case-sensitive systems, makefile) to set compilation choices.
However, writing
    TRANSLATION := de_DE
    include Makefile
did not work, because py.mk would override the TRANSLATION := specified
in an earlier part of the makefiles (but not from the commandline).

By using ?= instead of := the local makefile override works, but when
TRANSLATION is not specified it continues to work as before.

1 files changed, 1 insertions, 1 deletions

diff --git a/py/py.mk b/py/py.mk
index acf5d127b..eeb3b8650 100644
--- a/py/py.mk
+++ b/py/py.mk
@@ -7,7 +7,7 @@ HEADER_BUILD = $(BUILD)/genhdr
 # file containing qstr defs for the core Python bit
 PY_QSTR_DEFS = $(PY_SRC)/qstrdefs.h
 
-TRANSLATION := en_US
+TRANSLATION ?= en_US
 
 # If qstr autogeneration is not disabled we specify the output header
 # for all collected qstrings.