Prague to CDG will be on Czech airlines, not Delta. It's probably a code-share flight #.

I'll let other speak to connecting in 90min. I'd not be concerned with that time just about anywhere, but I'm not risk averse.

> Prague to CDG will be on Czech airlines

Just as likely to be Air France.

90 mins is sufficient on most days. In air travel, there are few if any sure things.

Delta could be using Czech, Air France or KLM as the Prague connector. Since you did not specify which Delta hub is your international gateway in the US, it's hard to tell what your choice on the return flight might be. www.deltaair.com is fairly good about specifying the flight operators.
In my experience, connecting through Amsterdam for anywhere is more efficient than CdG. I would be more comfortable with 90 minutes in AMS to find the second departure gate, and for my luggage finding the next plane. However, you can look up maps of both airports to get an idea of how complicated the respective terminals may be for your plane change.
http://www.aeroportsdeparis.fr/ADP/en-gb/passagers/home/
http://www.schiphol.com/

I have made connections at CDG in far less time than 90 minutes due to a flight delay but it was a challenge. If you run out of time ask the people at security if you can go to the front of the line. I only request this when it's really urgent but they did allow me to do that.

After missing a connecting flight with more than two hours between flights, I would not risk another connection at CDG with less than a three-hour window. Personally, CDG is fine if your destination is Paris, but I would fly just about anywhere to avoid being routed through there again.

If the duear flight's DEPARTURE is between noon and 6 pm, your flight may well be delayed because air traffic often gets backed up in the early-mid afternoons. Unless you are connecting at the same terminal in CDG, I would not chance it, particularly if I had to hoof it from Terminal 2A to 2F or some such thing. 90 minutes may sound like a lot, but I was flying back to the States from Zürich via CDG. We sat on the tarmac in Zürich for an hour before taking off. Had the AF flight to Atlanta not been delayed, we would have been left in the lurch.

There was one funny footnote to our scramble. At the time I did not know the layout of CDG as well as I did later on. I followed advice from the CDG people and went, cattle like, to wait on the shuttle bus, which seemed never to come. There wre several loud Americans behind me shouting at the gate keeper, who I hope understood little of the insulting comments. One of the more outspoken ones yelled out that he was going write the president. I asked him which one. The answer: George Bush. Sic 'em big guy.