Localization support

首先检查现有的 i18n 分支以及 issue 中提到的 ParametricBuilder 和 CommandGraph 入口点，然后追踪硬编码的运行时消息以及命令注解的描述和帮助文本。将提议的 Java ResourceBundle 方案与当前行为以及九条评论中的讨论进行比较。完成的要求是形成一套已达成共识且灵活的本地化设计，覆盖内部消息和外部命令文本。

Intake should provide some sort of support for localizations. This affects two fields:

1. Internal localization: All hard-coded strings should be externalized in a Java ResourceBundle and some behaviour might need to be updated in order to work as expected in an localized environment. Some points might need discussion:
   • Intake has several internal runtime exceptions that the end-user should never see (e.g. ParametricException). These might not need localization.
   • It might be a good idea to allow users to alter or replace the internal localization logic by providing custom translations. In that case the two entry points are ParametricBuilder and CommandGraph.
2. External localization: The values in command annotations, specifically description and help, need localization support. The entry point here is the ParametricBuilder.
   • If localizations use key -> value relationships, as enforced by Java resource bundles, description and help methods would need to return the key. This contradicts the current behaviour where both methods return the actual value, so a support for that old, non localised behaviour is needed.

On both fields, the support should be as flexible as possible and do not enforce any specific way of handling Locales on the user.

Since I need localization support in MyWarp, I have implemented a limited localization support in my own Intake fork (i18n branch). I would be happy to contribute these changes in a PR so there is something to discuss about, if the general direction fits.