Your English is just fine!
I think the answer is it depends. If the plant was weak just because it was not cared for well, that will not affect the genetics of it and the seeds can produce a perfectly strong, healthy plant.
If the plant was weak, because it is not adapted to your climate/ conditions (e.g. desert climate plants planted in wet, humid area, plants that need acidic soil planted in alkaline soil, etc.), the offspring will still not be adapted to your climate/conditions and will still suffer. If the plant was weak because it is a genetic variation that lacks vigor (sometimes hybridizers in the pursuit of some rare color or characteristic, sacrifice some hardiness), then it will still lack vigor.
Hope this helps some!