I cannot find a place listing the mathematical notations per country. The symbols listed in wikipedia refer to english notations. (Even the french page for instance, reproduces the english symbol for parallelism).
This question is very similar but the answers focus on maths at a university level, I am looking for elementary maths symbols only (from wikipedia: "topics frequently taught at the primary or secondary school levels").
As a complete answer might be too long, I suggest each answer to focus on one country and to only highlight the differences with english notations (but maybe there are more efficient, better ways to organize the answers, maybe a community wiki would be appropriate?).
I start with french and will update the answer when I find out more differing symbols.
Last note: this should not be limited to symbols used "in line" but can also list symbols used on figures (like, for instance, right angles that are not marked/decorated the same way by german people as by english or french people)
Notations differing in french:
\begin{array}{c|c|c} \textbf{Theme} & \textbf{French} & \textbf{English} \\ \hline \textbf{Angles} & \widehat{ABC} & \angle ABC \\ \hline \textbf{Distance} & AB & \overline {AB} \\ \hline \textbf{Lines} & (AB) & AB \\ \hline \textbf{Numbers} & 1,23 & 1.23 \\ \hline \textbf{Parallel lines} & \newcommand{\frparallel}{\mathbin{/\negthickspace/}} (AB) \frparallel (CD) & AB \parallel CD \\ \hline \textbf{Triangles} & ABC & \triangle ABC \\ \end{array}
EDIT: the source for french notations is myself, as I studied maths in France from school to university and am now a french maths teacher (in France). Nevertheless I can provide examples. There's an open source maths book for school where you will find these notations, like here for lines, the next page for parallel lines, and there on the left you'll find notations for angles.