This question shows the problem of the different conception of what is a nation.
For many people in Germany, in these times (but it largely remains true, although the law on nationality has recently changed), you have no choice. If your mother tongue is germanic, you were german even if you didn't know it, even if you didn't even feel so. This is a matter of language.
This is what led to pangermanism : to unite all germanic people in one Reich.
For France and other countries, anyone born in France and wanting to share a common destiny in what is the country is french.
Ah, that last sentence sounds nice.
Too bad it isn't true.
From the mid-1699's down to at least 1945, France considered "France" to be anything the French-speaking center could conquer, buy or bully into joining.
Throughtout the later 1600's and 1700's, France repeatedly tried to conquer territory along the Rhine. Among the territories she forcibly annexed was most of Alsace and Lorraine. I've never heard that the inhabitants wanted to "share a common destiny" with France.
I hope i dont have to explain France's behavior during the Napoleonic Wars. I've never heard that the inhabitants of the many areas she conquered wanted to "share a common destiny" with France.
In 1866, Napoleon III was demanding Prussian acquiescence to "the borders of 1814", which would give France Karlsruhe, Koblenz, and Mannheim. Nobody asked whether the inhabitants wanted to "share a common destiny" with France.
In 1867, France was trying to buy Luxembourg from William III, whether the inhabitants wanted it or not. And it wasn't just Napoleon III -- even liberal opposition leaders were demanding that France declare war on Germany and take Cologne, Dusseldorff, and Essen. I doubt the inhabitants wanted to "share a common destiny" with France.
After WW1, France still was trying to absorb land from Germany (Saar and Rhineland), though she wasn't permitted to. I've never heard of the people expressing an overwhelmingly popular urge to be French.
In fact, after WW2 France briefly wanted to annex the Saar, though as recently as 1935, 90% of the inhabitants voted to go with Germany, only 0.4% to go to France.
So I think your characterization is off: actually, France considered "France" to be any land she could conquer and subject to Francization.
Until after 1914, Germany at least tended to limit its annexationist agenda to areas of predominantly shared language (even more limited than that: she annexed nothing from Austria, only took from Denmark the areas that had already demonstrated a desire to join German, and made no attempt to grab Luxembourg in 1870). France didn't even impose that type of limit on herself.
Edit: and then we have to consider what happened to those Alsace-Lorrainers who found themselves back inside France, but weren't sufficiently vocal about their supposed joy: committees de triage, epuration, being fired from jobs, discrimination, expulsion, flight.