HTML Tags Within Internationalized Strings In Polymer.dart

I am displaying internationalized strings within a Polymer element as follows:

<div>
  <span class="title">{{title}}</span>
  <br/><br/>
  <span class="subtitle">{{subtitle1}}</span>
  <br/>
  <span class="content">{{paragraph1}}</span>
  <br/><br/>
  <span class="subtitle">{{subtitle2}}</span>
  <br/>
  <span class="content">{{paragraph2}}</span>
</div>

... and have the following dart code:

@observable String title;
@observable String subtitle1;
@observable String paragraph1;
@observable String subtitle2;
@observable String paragraph2;

//...

void onUpdateLocale(_locale) {
  title = getTitle();
  subtitle1 = getSubtitle1();
  paragraph1 = getParagraph1();
  subtitle2 = getSubtitle2();
  paragraph2 = getParagraph2();
}

//...

getTitle() => Intl.message('MY TITLE', name:'title',
    desc: 'This is my title',
    args: [],
    examples: {'None' : 0});
getSubtitle1() => Intl.message('Subtitle 1', name:'subtitle1',
    desc: 'This is my first subtitle',
    args: [],
    examples: {'None' : 0});
getParagraph1() => Intl.message('This is my first paragraph',
    name:'paragraph1',
    desc: 'This is the my first paragraph',
    args: [],
    examples: {'None' : 0});
getSubtitle2() => Intl.message('Subtitle 2', name:'subtitle1',
    desc: 'This is my second subtitle',
    args: [],
    examples: {'None' : 0});
getParagraph2() => Intl.message('This is my second paragraph',
    name:'paragraph2',
    desc: 'This is the my second paragraph',
    args: [],
    examples: {'None' : 0});

Is there a way to combine title, subtitle1, paragraph1, subtitle2, and paragraph2 into one observable variable that includes the <br> and <span> tags in its value?