It is true that the Interim Manual will soon be replaced with BANA Foreign Language Guidelines. That puts us in a rather awkward spot for the moment. The final BANA document is currently in the final editing process and I have to tell you that the editor is me! After is it complete, it goes to BANA Publications, where it will be finalized and undergo a final review process.
You are doing exactly the right thing by using the new Braille Formats. Use that in conjunction with the present Interim Manual, which is available to you for the member price. It is still highly useful and should be used for issues unique to foreign language. You will find that most of the formatting in it refers you to the current version of Braille Formats--and that means use the new one. The actual symbols for accented letters will not be changing, so the Interim Manual is still absolutely valid for that and will remain so. The only real changes are in formatting. If you get to a formatting situation that you feel is not adquately handled in the Interim Manual and unclear or also not adequate in Braille Formats, please post that problem at this forum and we will be glad to offer a solution. There are some things that are simply not handled at all in the Interim Manual that will be in the new BANA Foreign Language Guidelines. I am authorized to advise of anything applicable in the new Foreign Language Guidelines. It's just that the print document itself is not yet ready for distribution.