Notification language

Hi,

I’ve installed the booking plug-in since a little more then a month. And in added some translations in the mail notifications. When I confirmed the booking the mail was send in the user’s language (the language they had selected on the website). But since a while the language is not specified anymore and it send these mails with all languages (see below).
Is there anyway to solve this?

Thanks in advance,
Tom

[:en]Hi [:de]Guten Tag [:nl]Beste [:es]Hola [:] {user_name},

[:en]Your booking request has been confirmed. We look forward to seeing you soon. [:de]Es freut uns Ihnen mitteilen zu können, dass wir Ihre Reservierung bestätigen können. Wir freuen uns auf Ihren baldigen Besuch. [:nl]Uw reserveringsaanvraag is bevestigd. We zien u graag op {date} in ons restaurant. [:es]Su solicitud de Reserva ha sido confirmada. Esperamos su visita. [:]

[:en]Your booking details: [:de]Ihre Reservierungsdaten: [:nl]Uw reserveringsoverzicht: [:es]Datos de su Reserva: [:]
[:en]name: [:de] Name: [:nl] naam: [:es] nombre: [:]{user_name}
[:en]{party} persons [:de]{party} Personen [:nl]{party} personen [:es]participantes: {party} [:]
[:en]on: [:de]am: [:nl]op: [:es]fecha: [:] {date}

[:en]Message: [:de]Nachricht: [:nl]Bericht [:es]Mensaje: [:]
{message}

[:en]This message was sent by [:de]Diese Mitteilungen haben sie vom [:nl]Dit bericht is verzonden door [:es] Este mensaje fue enviado por [:]{site_link} [:en]on [:de] erhalten [:nl] op [:es] el dia [:]{current_time}.

The page I need help with: [log in to see the link]