Make primary language configurable

[Onurbon]

The current code assumes in a few places that the primary language is English but some users have expressed interest in running the entire pipeline in a different language, without translating back and forth to English.

Most of the work needed to be able to run a pipeline in a different primary language will consist in writing new prompts in at language.

Then some changes in the front end may will be needed , e.g. here to ensure that we show the right language name and flag when the primary language is not English. This can be configured by introducing new top-level config parameters called something like primaryLanguage and primaryFlag.