There are pronunciation dictionaries on line. I have found them, in a case such as this, to be of only general help, not specific assistance.
This may help:
British: "sold-er", or "sold-der" with a distinct, if not long, "o", much as if the word "sold" had an "er" attached. The "r" of course, would generally be indistinct. There may be variations in Britain I am ignorant of.
North American: "sod-der", as if "sod" with a "der" attached. This seems the most common pronunciation.
Liquids like "l" and "r" have taken a beating in English over time. Most Americans will have to remember to place the "l" in "salmon" and the same for most Brits. It just isn't pronounced.
In the Eastern US I have heard such as "sew-duh" , "saul-der" (with a distinct "r") and "sawd-der".
If one did not want to attract attention in North America, "sod-der" with a distinct "r" would be the way to say it.