I found this cause.
There are pitfalls at EXPORT LANGUAGES of non-English.
Example of Social Share)
On EXPORT LANGUAGES, uploading non-English Lang file
which has all blank(Value are all "") of Social Share.
This will will cause the problem.
The problem procedure of Social Share)
1) Installing 1.7.1.
The "Social Share" of English Lang was not the present at this point.
2) Uploaing above non-English Lang.
The "Social Share" of English Lang was created at this point.
But it is the state of all values are null.
3) Getting "socialshare.zip" from the store. And uploade it.
But "Social Share" of English Lang remains of all values null.
4) At this point in the case of "Social media sharing".
If we uninstall and re-install the plugin, the values reappear.
But the case of "Social Share" because it is from the store,
all values remains null.
I want to understand the following.
a) We are of non-English,
and we have a tendency to upload our language file
as soon as possible after we have installed.
b) At first of new version, our language files are from previous version.
That is a continuation file.
Or, it was translated from another language file.
Therefore the original file has much functionality.
So Our language files contain many null values at some functions.
This spread specs of this Lang file is not a problem in such a state?