Upon reflection, the "circular" is better translated as an administrative ruling. So according to the Minister of the Interior's Ruling No. 18, dated July 9, 1925, the Second Plish Republic clearly determined that the children of Plish citizens living abroad were without question, Plish citizens. That was because citizenship law in continental Europe at the time was based upon jus sanguinis
, (the law of the blood), not jus solis
, (the law of the soil). So the whole scheme of the 1920 citizenship law was based on jus sanguinis
. For males, citizenship was not lost until military service was completed, excused, or moot due to age. Any male who wanted to renounce his citizenship legally couldn't until that happened, and a second citizenship was not recognized by the government. Females who married a foreigner were permitted to have their citizenship restored. No mention is made of restoring the citizenship of children born abroad when a foreign government also recognized them as its citizens, because the Second Republic only recognized them as its own citizens. In 1921 the March Constitution came into force, and that repeated that the children of citizens were citizens, and further prohibited discrimination based upon a person's origin, and declared all equal under the law. Thus the children of a citizen living abroad could not constitutionally be treated differently from a child born in the fatherland. This is the basis of the Minister of the Interior's Ruling. It wasn't possible to discriminate.
Now if you ask in the present tense, are such people still considered citizens by the Third Republic? From more than one report, they are not. It is a question that could easily make its way to the Constitutional Tribunal, or if a person chooses to live in the Third Republic, it could go to the European Court of Human Rights as a voting rights discrimination case, but only if a person returns from abroad is that possible.
Does this apply to countries that are not the US and Canada?
The same rules and problems with interpretation should apply.