add lang_header arg for specify language header values

[jdugh]

add lang_header arg in export def. lang_header can be used for specify the language for header values in excel/csv export (you can have _xml header values and _default values for submits datas). If not set, lang arg override lang_header arg value.

[coveralls]

Coverage increased (+0.007%) to 83.958% when pulling 4ee322d on jdugh:lang_header into 8628d7e on kobotoolbox:master.

[dorey]

Hi @jdugh . Thanks for the PR. Could you add a test that uses this column and shows how the values would change when this parameter is used?

Also, if I understand correctly what this does, it might make more sense to call it header_lang or header_language.

[dorey]

Suggested change

	tag_cols_for_header=None, lang_header=-1):
	header_lang=None,
	tag_cols_for_header=None):

[jdugh]

I think we cannot set None to default value for "header_lang" otherwise we cannot know if it is not set or set to None. And, if user call with : (lang=False,header_lang=None) I don't want to change value of arg header_lang. If user call with (lang=False) - header_lang is not set, I want to override header_lang with lang value for not change the current algo.

[dorey]

Ah yes. Thanks for reminding me of this. I will discuss this with the team and see if we can agree on -1 or a different solution.

[jdugh]

hi @dorey , do you know if you can agree a -1 value (or a different solution), and also, accept this PR in the futur ?

[jdugh]

Hi @jdugh . Thanks for the PR. Could you add a test that uses this column and shows how the values would change when this parameter is used?

Also, if I understand correctly what this does, it might make more sense to call it header_lang or header_language.

Ok thank you. I go to create the test and change the name to header_lang. Here and in KPI views.

[jdugh]

@joshuaberetta I have merge my PR with the master and I have change the -1 default value with a constant.

[jdugh]

Hi @joshuaberetta and @dorey,
Do you think this PR can be merge with master in futur ?

[jdugh]

Hi @jnm.
Do you have any feedback about this one.
(This is a little up 😅 - PR without merge conflicts and with some unit test 😅)

EDIT :
The main objective of this feature is to allow to specify the language for header values in excel/csv/... export :
the 'name' question in header, and the 'label' response (mainly for choices list) in the data.
Currently you can only have full data (header and data) with 'name' or with 'label' through lang key in export API.
My end goal is to be able to download the data through API, with this structure.

Otherwise, Unless I'm mistaken, the endpoint on KPI API : /api/v2/assets/<ID_STRING>/data/?format=json does not offer to recover the 'question name' in json key, and the 'label' in values. If we could imagine the same system on this endpoint, that would be great!