Adding every single character from a font file is very inefficient as most of those characters will never be needed.
The easiest way to handle localization (currently) is to create a Primary font asset that contains all the known characters used in the project for each given language or sets of languages.
For Latin based languages and since their character set is limited, you can create a Primary font asset that contains all of extended ASCII. Then create a few additional font assets that will contains Cyrillic, Greek and other potential subset and assign those as Fallbacks to the Primary for Latin languages.
For Latin languages (and depending on the font you select) a sampling point size of 72 with padding of 8 typically results in a nice look font.
For CJK and since their character sets are much larger, you will create a Primary font asset for each and then have several fallbacks for each of them as well.
For Chinese for example, your primary will contain all the Chinese characters known / contained in your project. Then for those unknown characters likely to come from user input, you will create 3 additional fallback font assets which will contains the remaining 8105 character defined in the Table of General Standard Chinese Characters. As a result, the first fallback will contain the 3500 characters from the list minus those already in your primary. The 2nd fallback will contains the next 3000 minus again those in the primary and lastly the third the remaining 1605 minus those in the primary.
For East Asian characters, a sampling point size of 36 to 48 is actually pretty good with padding value of 4 to 5. Try to keep the padding at about 10% of sampling point size.
When creating the Primary and Fallback font assets, keep in mind that they do not need to be using the same sampling point size and padding. So the Primary can be sampled at higher quality (since you know these characters are contained in the project / UI and menus) and then use a lower quality for the fallback since they will likely come from user input which is typically plain white text and smaller on screen where the higher quality won’t be noticeable.
The only important part is maintaining the same ratio of Sampling Point Size to Padding for the Primary and Fallbacks. For instance if the primary is using a sampling point size of 80 with padding of 8 then the fallbacks could be using sampling point size of 50 with padding of 5. Maintaining the same ratio will ensure the same visual appearance in regards to styling (outline, shadow, etc.) between the primary and fallbacks when using Material Presets.
I certainly understand this is more involved than you wanted but like many aspects of game development where we have to create efficient geometry / topology and UV mapping for models or bake NavMeshes or Lightmaps to achieve the visual results and performance we seek, the same is true for text which granted isn’t as cool as these other things still remain important.
Having said all of that, a hybrid dynamic SDF system is in the works and will make this process much simpler. The recommended workflow will still include creating primary font assets that contains all the known / used characters in the project for each language or sets of languages but you will be able to use fallback font assets (set to dynamic mode) where characters not covered in your primary or other fallbacks can be added into those font asset at runtime.
The idea is to have the vast majority of characters already baked in your primary and existing fallbacks thus providing best quality and performance while relying on the dynamic system for those few characters that were unknown and coming from user input where the performance impact here is not noticeable by users since human type slow.