I have seen posts over the years about multisensory/phonemic reading instruction in languages other than English, but I am not able to find resources right now - I'll do a bit more digging and if I find something I'll be sure to post.
As far as whether or not the speech and language pathologist can help - I'd say maybe. There are S&L in the US that are very well trained in both oral language and written language. In fact, a widely used reading for program for dyslexics was developed by a S& L Pathologist: LiPS. And there is a widely used writing program called EMPOWER that was developed by a Speech and Language Pathologist. The key is finding someone that is trained and experienced in using a proven reading program. The programs most often used to teach reading in English are: Orton-Gillingham, Wilson, LiPS and Project Read (at least in my area!). Again, I recall reading about a program for French, but can't remember/find it. (I actually was searching for my son to find out if there were a program for him to learn a second language!)
You may want to contact the International Dyslexia Association in Canada (specifically in Quebec, if this is where you live). They would have good resources on programs and practitioners.
It sounds like the testing that was given was more of a screen rather than a full evaluation. I would highly recommend that sometime soon you would get a full evaluation that looks at all areas of cognition and academics and uses standardized, normed testing. The evaluation should also look at the underlying skills for reading such as phonological memory and processing, overall processing speed, verbal and non verbal reasoning and organization. These are all important in understanding strengths, weaknesses and for diagnosing (or not) disabilities. In my area (Boston) the top evaluators schedule 4-6 months out. If it is the same in your area, you are talking about the end of the school year at best. Your Speech and Language Pathologist may be able to help you with referrals. The cost in my area ranges from $2500-$3500.
www.readingrockets.com is yet another resource that may help you understand the kinds of reading support he may need. It is encouraging that you are able to teach him the sounds using pictures. This is an example of multi-sensory. The programs I listed would use images, but also use fine and gross motor skills to help teach the rules. The idea is that if you use all pathways to the brain, the child will learn more quickly and will be able to recall the new concepts more fluently and accurately.
As far as help from the school - Straight Talk About Reading offers a number of approaches at the end of the book. This might be helpful to the school. My only concern is that if he truly has a problem, and eclectic approach may not be enough. His time would be more productive using a well -researched and proven systematic program that was developed by experts. But, as you wait, the ideas in "Straight Talk" are at least a start.
