In Scottish law, Intermediate Diets are defined as follows in its homepages of the Scottish government and the Judiciary, which I also listed for you below in the "Web reference":

Chapter 20: INTERMEDIATE DIETS

20.1 When an accused pleads not guilty to a charge or charges on a summary complaint the court will fix a diet of trial. It will also fix an intermediate diet, commonly for a date 14-28 days before the date for the trial. Intermediate diets were introduced in April 1996 because it was found that on the day fixed for the trial a large number of trials did not go ahead. This usually happened because of one or more of the following occurred:

the accused did not appear;
there was a plea of guilty;
the procurator fiscal was prepared to accept a reduced plea;
some witnesses had not been successfully cited or had failed to answer citations;
the defence was not properly prepared;
the court had set down too many trials for that day in which pleas of not guilty were adhered to, with the result that not all of them could be heard that day.

0.2 The intention was that the intermediate diet would sort out most of these difficulties in advance of the trial so that witnesses did not needlessly attend on the day of the trial in cases which would not be going ahead. In theory the intermediate diet should have resolved all or most of these problems in the great majority of cases.

20.3 In terms of section 148(1) of the Criminal Procedure (Scotland) Act 1995 the purpose of an intermediate diet is to ascertain:

"So far as is reasonably practicable, whether the case is likely to proceed to trial on the date assigned as the trial diet and, in particular - the state of preparation of the prosecutor and of the accused with respect to their cases; whether the accused intends to adhere to the plea of not guilty, and the extent to which the prosecutor and the accused have complied with the duty under section 257(1) of this Act."

根据苏格兰司法厅的法律词汇 In the Glossary of the Judiciary of Scotland -- （see the weblink below)

Intermediate diet: A hearing in summary criminal proceedings which allows the court to check whether the case is likely to proceed on the date assigned for trial. A purpose is to minimise inconvenience to witnesses etc. if the trial is adjourned.
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As you said, there is a Preliminary Hearing (not diet) before Intermediate Diet and then the Trial itself.

Preliminary hearing 是“初审”, 而 Intermediate Diet 不用 hearing 这个字 ，目的是处理不必要因素造成的审讯延误，好像证据不足、证人/被告人缺席等，因此需要决定一个正式审讯日期， 让所有有关人士同意一个审理日期，让审理在最好的准备情况下进行。

根据以上的定义和解释，我建议用：

中级预审

而 preliminary hearing 可以译为〈b>初级预审 以区别中级预审和正式的审讯 Trial.

Hope you find this helpful.




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Note added at 3 days8 hrs (2013-06-28 10:17:23 GMT) Post-grading
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一點點分享而已，不用客氣。