The image is true in the sense that it was not manipulated in its pixels, and it is true that it depicts mainly Roma people who set camp on the railway line in Paris. But the date of "meanwhile" is manipulative as it indicates present day 2018 Paris. Taken together, that is a "No. That picture with its caption is not 'true'."
The picture shows a shanty town on the Chemin de fer de Petite Ceinture:
Paris' former Chemin de fer de Petite Ceinture ('small(er) belt railway'), also colloquially known as La Petite Ceinture, was a circular railway built as a means to supply the city's fortification walls, and as a connection between Paris' railway termini.[…]
Re-use and Present state
Access to the unused rail tracks is forbidden, but enthusiasts explore it nonetheless, describing it as a quiet, natural garden space within Paris
"Forbidden" does not mean inaccessible though: How To Explore Paris’ Beautiful, Abandoned Railway.
The above picture in doubt is confirmed when looking at newspaper reports like:
Life in the new shanty town taking root on Paris's abandoned railway:
But a few hundred metres away, hidden behind a large metro ticket booth, a camp has taken shape. The 19-mile belt of Petite Ceinture has been derelict for several decades and its possible redevelopment has long sparked debate among environmentalists and entrepreneurs. Then, shortly after the migrant crisis hit Europe, the squatter’s camp took root. “I know there is a Roma camp just a few minutes walk from La Recyclerie, I think it is just straight down the rails,” says one of the cafe’s bartenders, “but I’ve never been there, nor said hello.”
With shacks made from wooden boards and sheets of plastic, and with numerous pans covering holes in case of rain, this 500-metre section of track is home to an estimated 350 people. The infrastructure is nonexistent: there is no electricity and no running water. Camp residents must make the walk to the municipal showers at Porte de Saint-Ouen, almost a mile away.
Many camp residents are Roma from Romania or Bulgaria, but as Philippe Gossens at the Ligues des Droits de l’Homme (League of Human Rights) explains, refugees from the Middle East also live here, after fleeing their homes and making their journey to Europe over the summer.
According to French law, anyone who trespasses on the Petite Ceinture is subject to a €3,750 fine and six months in prison – but the Reseau Ferre de France (the French Railway Network), which owns the abandoned railway, has so far kept silent on the camp and its future. In the first few months of 2015, though, French authorities destroyed 37 squatter camps and displaced more than 4,000 people, according to the Ligues des Droits de l’Homme (the League of Human Rights).
The Guardian, Tue 5 Jan 2016 12.42 GMT Last modified on Fri 11 May 2018 13.12 BST
See also Gurdian 2014: The Petite Ceinture: the battle over Paris's abandoned railway and Precarious Roma Village Of Northern Paris: A Few Cautious Considerations (December 2015).
This kind of news making the round is of course not very welcomed by the French authorities:
Paris police clear Roma from disused railway line camp
Police have cleared hundreds of Roma people from a slum-like camp built on a disused rail line in north Paris.
More than 350 Roma people had lived in the camp on La Petite Ceinture since mid-2015. Activists said many left early ahead of the police action.
The site belongs to the national rail authority SNCF.
France has one of Europe's toughest policies towards Roma. Most live in camps that are regularly demolished and every year thousands are deported.
Amnesty International urged city authorities to find a lasting housing solution for those evicted in Paris - saying they would become homeless in mid-winter.
BBC World 3 February 2016
The real and bigger problems to the present day in and around Paris have a more permanent structure and the problem zones are typically populated with French citizens. The name for these problem areas is "Quartiers Sensibles" (i.e. the poor Banlieues, often equated with or called "cités"). These are often equated with plain "slums" as well:
Macron Unveils Plan to Tackle Problems in France's Suburban Slums (2018):
President Macron laid out a series of concrete, actionable measures for the country's troubled banlieues, or suburbs — from more community policing, urban renovation, and educational support, to cutting through layers of bureaucracy, fighting drug dealing, and better communication with local mayors about suspected radicals.
Counting what is actually and commonly defined as slums, France as a whole seems to have an ongoing problem, although on a smaller scale than with the suburbs.
Le Monde: Ces 570 bidonvilles que la France ne veut pas voir (2017) discussed in English in France races to tear down its 570 squalid shanty towns but root problems persist and Outlining the global fault lines of the ‘slum’ narrative as:
“The 570 slums that France doesn’t want you to see”, drawing attention to the hundreds of informal settlements in France (113 in the Paris region alone) where 16,000 inhabitants live a marginal and precarious life.
The key difference to classify that picture circling now as not entirely "true" is that the actual conditions depicted are not "current events" in 2018 and that the more depressing scales of French problems lie elsewhere and that even when actual "slums" keep popping up, they are not as permanent as commonly believed and understood for "slums" or frozen in that picture, but relatively quickly evicted in general. Scandalous as these conditions are, nonetheless, they are also not exclusive to France.
That "meanwhile" in question was a rather short lived phenomenon captured in that photo. There may be very well relatively small slum-like "settlements" in Paris, and elsewhere, now. But the scenes in the picture are not to be found any more, and on that location depicted they are very unlikely to return there (A High Line for Paris, Only More So). As a "look at the scandalous news from Paris" picture this is manipulative in 2018.
As long as deprived citizens, migrants and refugees are treated like they are in Europe these shanty towns can pop up everywhere at any time.