Nice to have: Option to keep English original keywords as valid

When we have translated keywords and the original English keywords, the test run would fail because the English keywords are unknown.
Would be nice to have an option to make this current behavior as a strict mode, and have the option to allow mixed translation and English keywords the default.

For example:

mode=multi   # The default (or mixed)

or

mode=strict   # The exact translation (or single) (or exact) ....

Copy of https://github.com/MarketSquare/robotframework-seleniumlibrary-translation/issues/59 because it also needs support from PLC.

未指定文件或测试。首先追踪 PythonLibCore 如何验证已翻译的关键字以及如何公开配置选项，然后查看 github.com/MarketSquare/robotframework-seleniumlibrary-translation/issues/59 中相关的翻译 issue。完成的标准是：默认接受混合使用的已翻译关键字和英文关键字，同时严格模式继续拒绝英文关键字。