Streamline language-specific style guides to remove unmeasurable metrics and redundant guidance

Language-specific style guides are located here: https://gitlab.com/gitlab-com/localization/gitlab-duo-agent-translation-platform/-/tree/main/specifications/languages

Problem

After restructuring the system prompt !34 (merged) to remove redundancy , the language-specific style guides need similar cleanup. Several guides contain guidance that falls into three problematic categories:

1. unmeasurable quality metrics
2. workflow instructions that duplicate the system prompt
3. aspirational guidance the agent can not implement independently

See examples of each of the above categories in comment threads.