Hi from Paris,
I wish to add two comments to the very good answer of David Levine.

Always remember that before 1914, and from 1870, France was the sole Republic in Europe.
You can understand that other countries, which were Monarchy or Empire, weren't very open to young migrants (or their own citizen) promoting revolutionary ideas. 
So Paris became a special place were foreign activists could stay, as long as they didn't act again French state.
You could find there a melting pot of foreign students and poor workers elaborating their plans to export their ideas.
To David's list, I wish to add Anarchists and last but not the least, Bundists !
You know of course that Bundists were Secular Socialists Jews and that Bund (est. 1897) became the main political and union movement among Jewish workers in Polish interwar period. Here, in Medem Center of Paris, we transmit its spiritual heritage.

Now, concerning your Wenglenski family.

I repeat, and repeat and repeat again in this forum, search my previous posts where I gave precise instructions to obtain copies.

You have to search / ask only 4 French and free data basis to start your search of any ancestor who stayed a while in France :

• if he / she remained foreign citizen : do an inquiry to archives of department of foreign inhabitants, from 1920 to today : https://www.ofpra.gouv.fr/fr/histoire-archives/archives
• if he / she became French citizen : access to naturalization file kept by Archives Nationales. Each file contains 30 to 70 documents which have been collected to study and accept naturalization. Search if a person had been naturalized by reference of decree :
•                       before 1930 : https://gallica.bnf.fr/ark:/12148/cb32726274t/date
•                       after 1930 : https://gallica.bnf.fr/ark:/12148/cb34378481r/date?rk=85837;2 
•                                          I attach copy of the page concerning Hinda Wenglinski's decree. We could discuss why her husband isn't naturalized with her in 1926...
•  
• if he / she had any activity which could put this foreign person into scrutiny of "Sureté Nationale", a police service in charge of surveying political and union activities. For some too long reasons to explain here, these files were taken to Berlin by Nazi in 1940, then to Moscow by Soviets in 1945 and only given back to France in 1994. These archives are known as "Fond de Moscou" in French National Archives :
• https://www.siv.archives-nationales.culture.gouv.fr/siv/rechercheconsultation/consultation/ir/consultationIR.action?irId=FRAN_IR_050044&details=false&gotoArchivesNums=false&udId=root&auSeinIR=true
•                                          I attach copy of the page concerning Chaim Wenglenski, he had a file ...

Then, you can search vital records archives of Paris and other places, and all archives on Shoah in France.

Khavershaft
Bernard Flam
Archives & history of Medem Center - Arbeter Ring ( Bund / Workmen Circle in France)