A method for converting an input text with words containing at least one word in a first language and at least one word in at least one further language into a speech waveform comprising the steps of providing a first monolingual phoneme symbol resource of the first language, generating a target sequence of language dependent phoneme symbols including one or more first sequence of language dependent phoneme symbols and one or more further sequences of language dependent substitute phoneme symbols associated with the first monolingual phoneme symbol resource, where said generating includes the steps of identifying at least one specific further language for words which do not belong to the first language, adding at least one further monolingual phoneme symbol resource of the at least one specific further language, applying the first monolingual phoneme symbol resource of the first language for words in the first language to generate the one or more first sequence of language dependent phoneme symbols, applying the at least one further monolingual phoneme symbol resource of the at least one specific further language for words in the at least one specific further language to generate one or more further sequence of language dependent phoneme symbols, replacing the one or more further sequence of language dependent phoneme symbols generated for the at least one word of the at least one further language with one or more further sequence of language dependent substitute phoneme symbols associated with the first monolingual phoneme symbol resource of the first language, where said replacing includes the steps of assigning to each language dependent phoneme symbol generated for the at least one word of the at least one further language a language independent target phoneme symbol, mapping to each language independent target phoneme symbol a language independent substitute phoneme symbol assignable to a language dependent substitute phoneme symbol associated with the first monolingual phoneme symbol resource of the first language, wherein said mapping includes the steps of, searching in a predefined table of distances between language independent phoneme symbols for the language independent target phoneme symbol at least one language independent approximate phoneme symbol with a distance to the language independent target phoneme symbol below a given maximum distance, checking whether the at least one language independent approximate phoneme symbol can be assigned to a language dependent phoneme symbol associated with the first monolingual phoneme symbol resource of the first language and selecting from the at least one assignable language independent approximate phoneme symbol at least one language independent substitute phoneme symbol, substituting each of the language dependent phoneme symbols generated for the at least one word of the at least one further language by language dependent substitute phoneme symbols associated with the first monolingual phoneme symbol resource which are assignable to the language independent substitute phoneme symbols to generate the one or more further sequence of language dependent substitute phoneme symbols associated with the first monolingual phoneme symbol resource, deriving at least one target unit sequence corresponding to the target sequence of language dependent phoneme symbols, selecting from a waveform unit database of the first language a waveform unit sequence approximating the at least one target unit sequence, concatenating the waveform unit sequence to the speech waveform. identifying at least one specific further language for words which do not belong to the first language, adding at least one further monolingual phoneme symbol resource of the at least one specific further language, applying the first monolingual phoneme symbol resource of the first language for words in the first language to generate the one or more first sequence of language dependent phoneme symbols, applying the at least one further monolingual phoneme symbol resource of the at least one specific further language for words in the at least one specific further language to generate one or more further sequence of language dependent phoneme symbols, searching in a predefined table of distances between language independent phoneme symbols for the language independent target phoneme symbol at least one language independent approximate phoneme symbol with a distance to the language independent target phoneme symbol below a given maximum distance, checking whether the at least one language independent approximate phoneme symbol can be assigned to a language dependent phoneme symbol associated with the first monolingual phoneme symbol resource of the first language and selecting from the at least one assignable language independent approximate phoneme symbol at least one language independent substitute phoneme symbol,