Mixed Language Catalog Records

Question: Why are there non-English notes and subject headings on English-language cataloging records?
In the past, there were only English language cataloging records in OCLC. English language cataloging does not mean that the materials are only in English. It means that the cataloging data on the bibliographic record is in English. In other words, although the title of the material may be in a foreign language, the notes about the piece and the subject headings, etc. will be in English.
Then other national libraries, as well as major foreign libraries and foreign vendors, began to put their records in OCLC. These records were cataloged in other languages. Therefore the notes, summaries, subject headings, etc. are in other languages, making them difficult for our users to locate and understand in many cases. Furthermore, publishers began to put much more information into records. For example, a German vendor record may have a German summary of the work and perhaps German subject keywords.
It was the practice for English language catalogers to remove all the foreign language information when we cataloged the book for our English audience. We would translate the subject terms into LCSH and translate all the notes into English. We would then remove the foreign equivalents.
Most recently the trend has been to leave most of the foreign language information when we catalog the book. The main reason for this is that the foreign language information is already on the record, usually supplied by the publisher or another library, and it may be useful to our patrons.
For example, although we are adding English subject headings, the patron who after all is interested in a foreign language book, may want to see or keyword search the foreign subject terms. So we would leave the Spanish subject terms on a book that is in Spanish. Likewise, publishers now frequently provide summaries, sometimes taken from the jacket or back cover of the book in hand. Catalogers felt that, although they did not have the time to translate all these summaries, the patron probably would appreciate access to these summaries. Therefore, we are leaving them in the record.
This creates a hybrid catalog record. The only way you can tell if it is an English language catalog record is to check certain very common notes. For example, the bibliography note will always be translated into English. Furthermore, most records will have at least one English subject heading. Although these records may look a bit confusing to librarians, the added value of keyword terms to search and explicative text for the user is a great gain. As we all know, users want ever more information and without removing this data, which is already present in many vendor records, we are able to provide them with valued additional information.