Chinese transcription of foreign names and countries often results in long words that (in my opinion) stick out from the native lexicon significantly. There is general agreement that Mainland Mandarin is a stress-timed language, which means that some syllables are shorter than others. This is made most clear by the use of neutral tone in polysyllabic words such as 朋友. I would like to know if, from your experience, whether the neutral tone or shorter syllables occur in longer loanwords and transliterations such as 布拉德・彼特 (Brad Pitt), 斯洛伐克 (Slovakia), 阿司匹林 (Aspirin). Thank you for your input
I don't agree that "Mainland Mandarin" is a stress-timed language. Where did you get the "general agreement"? In addition, I think that Mandarin is Mandarin. The difference between "Mainland Mandarin" and "Taiwan Mandarin" is smaller than British English and US English.
Back to your question. Even the words/names are translated from other stress-timed language, one reads them character by character in a steady pace (so called syllable-timed). 布拉德・皮特 reads as 布/拉/德・/皮/特, not 布/拉德・/皮特 or something else. But since many educated Chinese know English very well, they may mix English words in directly when they speak. Nowadays, when one use a standard way to say, for example, 布拉德・皮特, it sounds OK but a bit out of fashion. So people, especially young people prefer to use Brad Pitt instead of 布拉德・皮特. Here the words are already English, not Mandarin or Chinese any more. 朋友 reads as 朋/友. Both characters take the same time to pronounce.
Don't trust websites, such as this. In the comment you already see it's full of mistakes.