Most speakers in today’s societies are bilingual or multilingual and linguistic research has shown that the grammatical systems of two or more languages interact in speech production and perception. The confrontation of two or more competing phonological systems and their phonetic realization leads to what we generally understand as a "foreign accent". The interference appears on the segmental and the prosodic level. Research in second language acquisition has previously focused on segmental features while research on prosody and its important role in language learning is rather scare. This present paper examines the intonation of Belfast English produced by native speakers and two groups of German second language learners of English. Acoustic prosodic characteristics responsible for the perception of a foreign accent are identified as deviations in the nuclear pitch patterns. Using production data the study aims to examine the occurrence of regional marked intonation patterns in different speaking styles. The study provides (1) evidence that specific regional intonation patterns are acquired in a naturalistic setting, (2) that these patterns are transferred into different speaking styles in second language production whereas regionally marked intonation patterns vary according to the formality of the speaking style in native language production.