RTLCss is a tool intended to be used as a global package not as a dependency, you give it a LTR based stylesheet, and you get the corresponding RTL css. It has also a CLI which simplify the process:
RTLSCss CLI Guide.
As for handling the RTL direction with ngx-translate, I had a "dir" property in each language .json file that had a value of "ltr" or "rlt", see this plunker:
https://plnkr.co/edit/oPXmAS?p=preview
With that"dir" property, you can either set a global container div that has an attribute dir with that "dir" value, and also add a special class to it if that value is "rtl" (refer to the previous plunker).
And you can set any special css properties that you have for the "rtl" languages (font-family, size ...).
@Component({
selector: 'my-app',
template: `
<div dir="{{ 'dir' | translate }}" [class.rtl]="('dir' | translate) === 'rtl'">
<h2>{{ 'HOME.TITLE' | translate }}</h2>
<label>
{{ 'HOME.SELECT' | translate }}
<select #langSelect (change)="translate.use(langSelect.value)">
<option *ngFor="let lang of translate.getLangs()" [value]="lang" [selected]="lang === translate.currentLang">{{ lang }}</option>
</select>
</label>
</div>
`,
styles: ['.rtl { color: red; }']
})
If you don't want to use a global div and want to set this in the body tag you'll have to inject a rendrer in the app.component like stated in this answer: Angular2 add class to body tag