My question is: I have a very bright six-year-old in a private school. Starting at what age should I supplement her language arts skills? I know that there are some private schools that offer writing courses in the summer for kids entering the first grade. I am not a parent that pushes, only challenges. She has been taking German as a foreign language since she was three.
While speaking and reading a foreign language are often the primary goals, foreign language instruction also provides great opportunities to learn about the cultures of other people who speak the language. Learning Italian or German opens the door to attending operas in those languages; learning French enables one to read the literature of a variety of countries. Most future leaders in business and government will need to function in a global community where mastery of other languages and cultures is a must. Not to mention that knowing Japanese makes traveling in Japan a whole lot easier.
Some in the field of gifted education (Joyce Van Tassel-Baska, for example) suggest Latin instruction as a good foundation for all languages and for learning grammar. In truth, exposure to more than one language will reinforce mastery of syntax for gifted students as they will note logical consistencies within and across languages. You may want to look at my answer to the Mom that wrote in about her daughter who is a budding writer for ideas about encouraging good writing.
To supplement formal language instruction, I would encourage you to investigate getting your daughter a pen pal from another country or inquiring at her school about other children from Germany with whom your daughter might play. Of course, older students in high school can host exchange students from other countries, as well as study abroad once they are in college.
By the way, the 60's are still pretty fresh in my memory. I'm one of those "took Latin, diagrammed sentences, wrote research papers" kind of people. I hope it shows!